Creating rooms and connecting rooms always creates two exits: from the room you're currently in to the other room, and another exit from the other room back to the room you're currently in. Deleting an exit deletes only one of the two, thus introducing one-way exits. Be aware of that and make creative use of it. 😄

Exits can also have conditional reveals, so you can build riddles using exits. For example, if there is a diary, that tells you to look for a secret trapdoor, then the “diary” thing has an id which you get using “id diary” and the “trapdoor” exit is hidden using “hide trapdoor” and revelead only if you’ve read the diary using “reveal trapdoor for 345” (assuming that 345 is the id of the “diary”).