I've been to Izu to see Kawazu Nanadaru (meaning seven waterfalls) last weekend.
The area is the location of the novel called "The Izu Dancer" by Yasunari Kawabata.
It is really a good place to get refreshed!
Kawazu is also famous for cherry blossom.

Getting stayed in Toi Fujiya Hotel.
I had a sashimi Tenagaebi (Metanephrops japonicus, Japanese small lobster) which is the best one I've ever had!!!
(They are at the ends of Funamori, sashimi boat)
Surely onsen are awesome.
Some rooms are equiped with private open-air onsen.