An underground lair has stable temperature, doesn't need heating really 😀
Discussion
True, but some might need it for dehumidification, depending on local climate and geology.
Not every underground doomer/villain lair can be built into a salt dome under Mount Olympus :)
Yes humidity might indeed be an issue. But it is ok then for aging your wine 😀
Need? No. But I certainly do *prefer* a temperature above 16°C.
It's nice after coming in from a hot day on the surface in the summer, but in the winter it doesn't exactly feel "warm". 🤣