[LVL ED] New Question: How to create a door

[Cruzore]

For 1 & 2:
Under Entities>Special, there is the cave_in as an entity. So it has a active checkbox. This way you can set it inactive, set it active when you need to, add some sound and you got your cave in.
For the 3rd:
Under Entities>storage, you can use all bookshelves. Just use a AddUseItemCallback(look on the engine scripts page on the wiki for details) and you can set the shelf inactive as a result. Might want to either let the player fadeout, or force him to watch somewhere else, since seeing a shelf disappear is not that good.
I am pretty sure there are other soultions for 3, but this is one.