One shot suggestion...

A single temple/dungeon. It's what I did to decide if I wanted to go on to eventually dm a campaign. It was a three level temple with enemies on each level in multiple rooms, a ceiling in one room that lowered (think of Indiana Jones style trap) that you had to solve a puzzle to get the ceiling to go back up, and a sphinx whose answer you had to get correct to get out of the temple, and then the temple simply disappeared. There was a ghost/death knight, an intellect devourer in one room, a broken wall, and two hidden rooms. I did it during my husband's campaign so he could have a break and get to be a player. And the temple disappeared so he could tie in anything he wanted or treat it like it has been a mass dream.