It is warmer
It was warmer in the cavern than outside. It was 42 degrees outside when I went and I had to take off all my winter clothes inside.
No we were there in Dec. I think they heat it no problem, you might want to call them
Naturally its cooler under ground in general, when I went in the summer it was very cool and comfortable, it's a decent walk - the entire cavern, and I'm pretty sure the temperature is regulated. So I would say, it will be cool but not freezing.
No, the temperature is pretty consistent and comfortable. But, wearing a sweater will probably make you feel more comfortable if this is your first time underground.
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