Our Djungarian hamster is apparently getting hot when temperatures reach about 25 °C. She then sleeps outside her house, in a corner of her terrarium, leaning on the glass and looking annoyed. She also tried to dig deeply, probably an instinct to make a hole deep enough to get into colder regions of soil.
As the weather will get even hotter during the summer and we don't have air conditioning, what could we do to make the hamster feel better? Would it help to add some small fan (like a computer cooling fan) to circulate air in the terrarium? Or add some rocks or other objects outside and inside her house with higher thermal conductivity, so that she could cool herself down by leaning on them?