There's a Noh Mask Museum in Tokorozawa, near the Koku Park. I've never been in it, they close pretty early, but will have to find the time to someday.
Don't know much about Noh (Guide to Noh), but I think it's one of the oldest types of theater...kind of like a musical. The masks that they wear are one of it's features.
The museum is open every first and third Saturday & Sundays from 11am to 5pm. The admission fee is 300yen.
