A daylight basement or a "walk-out basement" is contained in a house situated on a slope, so that part of the floor is above ground, with a doorway to the outside. The part of the floor lower than the ground can be considered the true basement area. From the street, some daylight basement homes appear to be one story. Others appear to be a conventional two story home from the street (with the buried, or basement, portion in the back). Occupants can walk out at that point without having to use stairs. For example, if the ground slopes downwards towards the back of the house, the basement is at or above grade (ground level) at the back of the house. It is a modern design because of the added complexity of uneven foundations; where the basement is above grade, the foundation is deeper at that point and must still be below the frost line. Full-size windows can be installed in a daylight basement. These can provide exits for bedrooms (building bedrooms in basements is usually illegal without an outside escape). Ventilation is improved over fully buried basement homes, with less dampness and mould problems. Daylight basements can be used for several purposes – as a garage, as maintenance rooms, or as living space. The buried portion is often used for storage, laundry room, hot water tanks, and HVAC. In a look-out basement, the basement walls extend sufficiently above ground level that some of the basement windows are above ground level. Where the site slopes gently and is insufficient for a walk-out basement, a look-out basement tends to result. Sometimes, a look-out basement is deliberately constructed even on a flat site. The advantage is that the basement windows are all above grade. The disadvantage is that the main floor entry is above grade as well, utilizing stairs to access the main floor. The raised Bungalow design (known as a split-entry home in much of the US) solves this by lowering the entry halfway between the main floor and basement to make a dramatic, high-ceiling foyer. It is a very economical design because the basement is shallower, and excavation costs are reduced. A “walk-up” basement is any basement that has an exterior entrance via a stairwell. Some designs cover the stairwell with angled “basement doors” or "bulkhead doors" to keep rain water from accumulating in the stairwell. When initially built, the main floor joists are often exposed and the walls and floors concrete (with insulation, where appropriate). Unfinished basements allow for easy access to the main floor for renovation to the main floor. Finishing the basement can add significant floor space to a house (doubling it in the case of a bungalow) and is a major renovation project.

Pipes:
A pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases (fluids), slurries, powders and masses of small solids. It can also be used for structural applications; hollow pipe is far stiffer per unit weight than solid members. The major categories of plumbing systems or subsystems are: potable cold and hot tap water supply, plumbing drainage venting, sewage systems and septic systems with or without hot water heat recycling and greywater recovery and treatment systems, fuel gas piping and hydronics, (i.e. heating and cooling systems utilizing water to transport thermal energy, as in district heating systems).

Utility Tunnels:
A utility tunnel, utility corridor, or utilidor is a passage built underground or aboveground to carry utility lines such as electricity, water and sewer pipes. Communications utilities like fibre optics, cable television and telephone cables are also sometimes carried. They may also be referred to as a services tunnel, services trench, services vault, or cable vault. Smaller size cable containment is often referred to as a cable duct, or underground conduit. Direct-buried cable is a major alternative to ducts or tunnels. Utility tunnels are common in very cold climates where direct burial below the frost line is not feasible (such as in Alaska, where the frost line is often more than 5.5 metres below the surface, which is frozen year round). They are also built in places where the water table is too high to bury water and sewer mains, and where utility poles would be too unsightly or pose a danger (like in earthquake prone Tokyo). Tunnels are also built to avoid the disruption caused by recurring construction, repair and upgrading of cables and pipes in direct burial trenches. Utility tunnels are also often common on large industrial, institutional, or commercial sites, where multiple large-scale services infrastructure (gas, water, power, heat, steam, compressed air, telecommunications cable, etc.) are distributed around the site to multiple buildings, without impeding vehicular or pedestrian traffic above ground. Due to the nature of these services, they may require regular inspection, repair, maintenance, or replacement, and therefore accessible utility tunnels are preferred instead of direct burying of the services in the ground. Utility tunnels range in size from just large enough to accommodate the utility being carried, to very large tunnels that can also accommodate human and even vehicular traffic. Utility tunnels are often installed in large industrial plants, as well as large institutions, such as universities, hospitals, research labs, and other facilities managed in common. Shared facilities, such as district heating, use superheated steam pipes routed through utility tunnels. On some university campuses, such as the Massachusetts Institute of Technology, many of the buildings are connected via large underground passages to allow easy movement of people and equipment. Some municipalities, such as Prague in the Czech Republic, have installed extensive underground utility tunnels, to allow installation and maintenance of utility lines and equipment without disrupting the historic streets above.

Subways:
In England and Wales, the Republic of Ireland, Hong Kong and Commonwealth countries such as India, South Africa, Australia and New Zealand, a subway is normally an underpass for pedestrians and/or cyclists beneath a road or railway, allowing them to reach the other side in safety.
n the US, the term "subway" means an underground rapid transit system, and the term pedestrian underpass is used for a passage beneath a barrier. Rail station platforms may be connected by pedestrian tunnels or footbridges.
Rapid transit, also known as metro, subway, underground, or colloquially as "the train", is a type of high-capacity public transport generally found in urban areas. Unlike buses or trams, rapid transit systems are electric railways that operate on an exclusive right-of-way, which cannot be accessed by pedestrians or other vehicles of any sort, and which is often grade separated in tunnels or on elevated railways. Most rapid transit trains are electric multiple units with lengths from three to over ten cars.[40] Power is commonly delivered by a third rail or by overhead wires. The whole London Underground network uses fourth rail and others use the linear motor for propulsion. Most run on conventional steel railway tracks, although some use rubber tires, such as the Montreal Metro and Mexico City Metro and some lines in the Paris Métro. Rubber tires allow steeper gradients and a softer ride, but have higher maintenance costs and are less energy efficient. They also lose traction when weather conditions are wet or icy, preventing above-ground use of the Montréal Metro but not rubber-tired systems in other cities. Crew sizes have decreased throughout history, with some modern systems now running completely unstaffed trains. Other trains continue to have drivers, even if their only role in normal operation is to open and close the doors of the trains at stations.

A storm drain, storm sewer (US), surface water drain/sewer (UK), stormwater drain (Australia and New Zealand), or simply a drain or drain system is designed to drain excess rain and ground water from impervious surfaces such as paved streets, car parks, parking lots, footpaths, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems. They are fed by street gutters on most motorways, freeways and other busy roads, as well as towns in areas which experience heavy rainfall, flooding and coastal towns which experience regular storms. Many storm drainage systems are designed to drain the storm water, untreated, into rivers or streams. Some storm drains lead to a mixing of stormwater (rainwater) with sewage, either intentionally - in the case of combined sewers - or unintentionally.

A combined sewer is a sewage collection system of pipes and tunnels designed to also collect surface runoff. Combined sewers can cause serious water pollution problems during combined sewer overflow (CSO) events when wet weather flows exceed the sewage treatment plant capacity. This type of sewer design is no longer used in building new communities (because current design separates sanitary sewers from runoff), but many older cities continue to operate combined sewers. While most sewers are no deeper than 4 metres, really deep drains can extend down to 90 metres

A "dungeon" is traditionally located underground, and no part of the Underground fails to qualify for the term in that respect. For the purpose of adventuring in the Underground, a dungeon is any locale or extended area that offers the possibility of adventure, danger, and treasure. By this definition, the Underground contains literally hundreds of dungeons. Dungeon Crawling is the act of exploring a dungeon (or other dangerous area) while looking for treasure or some other important object. The characters must battle enemies (usually monsters) and use their skills and equipment to negotiate obstacles (usually traps).

There are a number of problems associated with the construction of the vast underground complexes required in a dungeon based campaign. At first glance, each of them seems to be more than adequate justification for the abandonment of the dungeon setting as wholly impractical. As you might imagine, building a dungeon of any significant size is a very time consuming process. If two structures of equal size are commissioned, one built on the surface and one underground, the surface construction will almost certainly be completed first. The reasons for this are manifold, but centre primarily on the difficulty of working beneath the surface of the earth. Just as underground
construction is a time consuming process, so too is it an expensive one. In addition to the normal costs for an above ground structure, complexes built below the surface must have large quantities of earth removed and carted away. Further, money must be allocated for the special equipment which is used to pump out flooded areas or keep air circulating so that workers can survive. Further, sections of tunnels which might collapse must be shored up and steps must be taken to counter the myriad other hazards unique to dungeon excavation. Working underground is very hazardous. As such, accidents are common enough and workers are frequently injured, disabled, or even killed. Persuading people to work in such an unsafe environment is not easy and often requires a considerable outlay of cash. The time lost to worker injuries and the cost of securing labourers for above ground construction projects is far
less than it is for underground ones.