Posting here because this thread is relevant and has a lot of useful info and links. Question for the crowdsourcers here. I'm thinking of heading to Mt. Koya in the middle of winter, early February. Is that a foolish endeavor? Are we talking really cold?

Foolish? Not at all; Oku-no-In was hauntingly beautiful with all the snow-covered tombstones. The snow also dampens all sound and with the lack of crowds, makes for a very quiet, peaceful walk.

Whenever I went up there in the winter, it wasn't all that bad. I must admit that I had the flexibility to specifically go on windless, sunny days though. I imagine it would be a lot more brutal if the temp plunged or there was a wind chill effect. Just remember to layer. There were a couple of times when I was freezing going up the cable car but was sweating up there at noon with the sun beating down on me.

I was there in the spring and didn't feel cold, although I wore a sweatshirt indoors the whole time, but I did notice that my room was stocked with heavy blankets (that had sutras printed on them).

It can be pretty cold up there in the Winter, but as in many spots in Japan, there is a certain beauty to the winter scenery. Most important is to dress warmly, and stay dry. Enjoy your time up there.

Well, it was sunny and windless, but it was still cold. Not raw cold, but cold enough for Mrs. Pickles to stop feeling her toes under her winter boots and her fingers under her gloves after a couple of hours of walking around.

On the upside, it is very pretty in the snow, and there were very few people there. The Hanabishi restaurant was very good.

Sounds about right. Pretty cold, but also very attractive with the winter scenery, and not busy. Overall, sounds like you had a good time though.