Question

which key detail helps you understand what makes the icehotel different from most other buildings?
it melts when spring comes.
visitors stay in it every year
it is open during the winter.
people built it in a small town.

Explanation:

Most permanent buildings do not melt seasonally. The Icehotel's unique trait is that it is constructed from ice and snow, so it melts when temperatures rise in spring, which sets it apart from typical non-temporary structures. The other options describe features that are not unique to the Icehotel.

Answer:

It melts when spring comes.