[Josh Grisdale]

Maybe @wanping knows a bit more, but according to this you can watch the yumomi in a wheelchair:

https://www.kusatsu-onsen.ne.jp/netsunoyu/0001.html

Not a lot of detail! So might want to contact them directly.

This blog also mentions going and there were no steps and the staff were kind.

https://www.z-z.jp/thbbs.cgi?id=kokofurig&p3=&th=119