The boundary between exploit and creative play is very fuzzy. Here's an example that came up in my game:
Situation: a few characters hit a teleport trap and found themselves inside a small cell with transparent walls of force, in the middle of an otherwise big open area. They could see there were no immediate threats outside the cell, but had no way to escape (it's intended as a pure death trap; you get stuck in there and unless you've got some sort of dimension door or teleport or similar available, you eventually starve).
Nobody has any of those effects available but a caster does have Rope Trick. So, she casts Rope Trick and everyone climbs in. Rope is pulled up and then (and here's the creative bit) because there's nothing saying the rope always has to be lowered out of the middle of the "floor" of the little demi-plane it's instead lowered out of a corner, outside the cell wall! Everyone climbs down, and then they just have to worry about getting back to where they came from.
Exploit, or creative play?