My two younger sons and I have a different kind of D&D 5th edition campaign going. The campaign takes place in a mega dungeon. Each session we switch off as Dungeon Master. Whomever is playing characters for the next session decide which exit they are going to follow. The D.M. who is up maps out a new room and then designs one encounter in the room.
We play the dungeon on average about every other day after dinner. The session usually last 15 to 25 minutes.
It is a great way to spend some time with my sons. The boys get to play and D.M. a little bit and my youngest gets to let his imagination run wild designing his encounters. We very rarely run into a standard monster in his encounters. Nobody gets burned out as D.M. or just playing.
We use a shared google doc for the room descriptions. One of my favorite encounters my youngest son wrote was when we ran into a scorpion the size of a taxi with a stinger the size of a long sword. Fun times!