The Ropeway
It's easy enough to walk up the hill to the castle of course, that is if you are reasonably fit, but equally as fun to get the ropeway up.
260 yen one-way. At the end of Okaido, cross over and walk up the well signposted road to the ropeway station.

Dogo Onsen Spa - 3,000 year history
Delicious food