When an explorer lands in a barrier room from above, which side do they end up on?
If it is the Vault you always appear on the outside, otherwise it is your choice as to which half of a barrier room you appear on.
From the official errata &amp; FAQ:

Collapsed Room -- If you land in a room with two parts, such as the Chasm, which half do you land in?
If anything transports you to a barrier room, you decide which side of the room to end up in. If the arrival causes a counter to be created, as with the Collapsed Room or the Secret Passage, then that counter is permanently on the side of the room you choose. Anything that takes you to the Vault, however, always leaves you outside the door.