09-10-2023-2048 - draft (burial vault (tomb), sinkhole, underground base, etc., draft)

An underground base is a subterranean facility used for military or scientific purposes.

Examples are:

• Cheyenne Mountain Complex
• Chiashan Air Force Base
• Iranian underground missile bases
• Raven Rock Mountain Complex
• Zeljava Air Base

There may be more than 10,000 underground military facilities worldwide.^[1]

^{https://en.wikipedia.org/wiki/Underground_base}

The Red Lake sinkhole in Croatia

A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are locally also known as vrtače and shakeholes, and to openings where surface water enters into underground passages known as ponor, swallow hole or swallet.^[1][2][3][4] A cenote is a type of sinkhole that exposes groundwater underneath.^[4] Sink and stream sink are more general terms for sites that drain surface water, possibly by infiltration into sediment or crumbled rock.^[2]

Most sinkholes are caused by karst processes – the chemical dissolution of carbonate rocks, collapse or suffosion processes.^[1][5] Sinkholes are usually circular and vary in size from tens to hundreds of meters both in diameter and depth, and vary in form from soil-lined bowls to bedrock-edged chasms. Sinkholes may form gradually or suddenly, and are found worldwide.^[2][1] 

https://en.wikipedia.org/wiki/Sinkhole

Tomb of the French King Charles X, and his son Louis, in the Franciscan monastery Kostanjevici, Nova Gorica, Slovenia.

The Brisbane family vault, in the graveyard next to Skelmorlie Aisle, Largs.

A burial vault is a structural underground tomb. It houses the casket and protects them through a lined, sealed container. A burial vault shields the casket from maintenance equipment and resists water. Different levels of burial vaults are offered, such as premium, basic, and standard protection.^{[1][better source needed]}

Wikimedia Commons has media related to Burial vaults.

It is a stone- or brick-lined underground space or 'burial' chamber for the interment of a dead body or bodies. These burial tombs were originally and are still often vaulted and usually have stone slab entrances. They are often privately owned and used for specific family or other groups, but usually stand beneath a public religious building, such as a church, or in a churchyard or cemetery. A crypt may be used as a burial vault.^{[citation needed]} 

https://en.wikipedia.org/wiki/Burial_vault_(tomb)