Ancient shrines, commonly referred to as Ancient dangers due to the event card, are large structures that spawn on the map upon generation. They take the form of massive unexplored rooms.
The walls of the shrine are always undamaged and in perfect condition (unless it was damaged somehow after map generation, raiders will ignore the walls of the shrine). If they are damaged, they are most likely ruins.
Having a colonist walk by the walls of the structure will trigger an Ancient danger event prompting:
"As (Colonist Name) draws near the ancient wall a sense of foreboding overcomes him. (S)He isn't sure why, but (s)he feels this dusty structure may contain great dangers"
Ancient shrines are large rooms built of undamaged stone or steel walls (if they are damaged, they are almost certainly part of a ruin) partially or completely under a mountain that contain at least one of the following: ancient cryptosleep caskets, artifacts such as psychic animal pulsers or psychic insanity lances, bug hives, luciferium or mechanoids. Due to being fully enclosed, one cannot see within the room (except for corners with hives), and hovering over the grayed out area as seen in the picture will only say 'Undiscovered' in the bottom left corner. The only way to find out what is inside is to deconstruct a wall section or blast a hole in. It is highly suggested to take the latter option, however, because deconstructing requires the pawn to touch the wall, and if you're unlucky enough, a scyther is on the other side waiting for you. Haulers are also discouraged to open these rooms as they may attempt to take the stone blocks from the deconstruction, exposing themselves to hostiles within. When selecting a character to deconstruct, make sure to toggle its mode from Attack to Flee or it may engage hostiles instantly against your will. Ancient shrines are not guaranteed to spawn on small or medium maps but will always spawn on either of the large map sizes. Two or more may spawn of one of the largest map sizes.
The ancient shrine will contain ancient cryptosleep caskets, described below, tables of different sizes, columns, and/or urns. The floors will generally be made out of flagstones, steel tiles, or just stone tiles. The shrine can also provide a decently clean room (after any slime or dirt from ancients or bugs have been room) for a kitchen or hospital earlier in the game.
Ancient Cryptosleep Caskets
Each casket contains either a human belonging to one of the Ancients factions, an ancient and a megascarab, a group of megascarabs, or nothing. The humans can be neutral or hostile, and can also spawn wounded, downed or dead. All caskets open simultaneously when any one of them is manually opened or attacked. Once opened, those capable of walking may start to wander around, others will try to escape to the map edges or attack your colonists. Anything living that emerges will be afflicted with cryptosleep sickness. If captured, these people typically have a low recruitment difficulty.
These spacers can spawn with synthread and hyperweave clothing, power armor, or may be naked. They can be equipped with an industrial or spacer weapon, and sometimes come with plasteel, components, and gold in their inventories which drop when they are downed, captured or stripped. See the Ancients page for details. Characters recruited will be added not last in the colonist bar as with common recruits but, after your starter colonists and before any other incorporated later on to the roster.
These spacers can be taken advantage of, providing your pawns assault weaponry, armor, and some precious gold that is eventually used for the multi-analyzer. early in the game. To do this, the ancients should not be shot, but be downed by heat. This can be achieved by raising the temperature of the shrine to ~200° Celsius, but not above 270°, as items will spontaneously combust. The caskets should be then shot at by a pawn standing between opened doors, slowing the rate at which heat escapes from the room. After the caskets are opened, close the door. The ancients will quickly be downed by the heat, but some hostile ancients may die due to the "enemy death on down chance" setting in the game. Both types of ancients may also kill each other in the time it takes for heatstroke to reach 60%, or extreme severity. Once severity reaches around 70%, you can strip and capture the pawns.
These caskets can be claimed and used later by your colonists. Thus, ancient dangers may be worth opening specifically to utilize them - such as when one of your most valuable pawns is dying from a disease in the early game or when an addicted pawn has run out of luciferium. Deconstructing the caskets yields steel and a small amounts of the somewhat rare resource uranium.