Yurari close to Kawaguchiko town is a great Onsen to visit.
You can enjoy the mineral baths with the Mt. Fuji right across your eyes.
After you finish your bath I recomand to take massage. It is only 60.000 Y for 60 min and it is really great.
A popular place for viewing Mount Fuji and Lake Kawaguchi below. It can be very crowded but the view is spectacular. There is a cable car from the lakeside or you can walk to the summit. I'm far too lazy but I saw plenty of senior citizens who walked up so it couldn't be that difficult.
Probably 75% of people who climb Mt Fuji do so in order to catch the sunrise, so why not avoid the crowds and see the just as spectacular sunset?
A friend and I hiked from Kawaguchi-ko to the summit, taking 12 hours, and arrived just in time for the sunset. Considering it was the first day of the "season", we were the only ones up there at the time as well!
We were then treated to watch all the hordes of night-climbers coming up on our way back down, being glad we were not part of the crowd!
If you are in Kawaguchi-ko, it's worthwhile taking a trip up the hill on the ropeway. One one side, there's a good view of the lake, and on the other, a great view of Mt. Fuji.