For one of the mountain biome structures.

There could be abandoned vaults referencing the fallout game series. as there are abandoned vaults some of them could be heavily damaged but are much bigger than abandoned ones also in these damaged vaults there can be destroyed prototype end portals that the player can use to create there own end portals late game but because these are prototypes there can be a risk of it blowing up upon activation or jumping in to many times. Other advanced technologies could be found in very rare specialised vaults that were used as research facilities.