Players are zapped to new low-magic fantasy world minus their memory and anything metal they were carrying (If you are a kindly GM give magic stuff a save to make the trip) and sporting a few new wounds (Its fun to describe their injuries). In this new world they are poor, ill-equipped, injured, they don't speak the language(s), their spells don't seem to work as well and nobody likes the way they smell or they way they look ("Why's that short guy got pointy ears?").
I ran this adventure by starting them in a cavern that looked like the start of an underground temple complex and stuck a cave-in at the entrance to the complex. I then suggested their last memories involved ransacking an underground temple of some kind. This accomplished a few important things:
The reason I made the new world low-magic was to short circuit magical short-cuts. The cave-in, the language barrier and other fun stuff could have been circumnavigated by the right spells.
Run correctly this can be a really hard adventure, going into a new world with little to no resources and little recourse to magic will really stretch your players inventiveness.