We are staying there in mid-July. I wonder if anyone has any tips on what not to miss and nice areas to see on the lake. Thank you.
You of course must not miss Orvieto and it's gorgeous cathedral/duomo, which was built to display the relic of the bloody cloth from a miraculous communion service held in Bolsena in 1263. And the nearby tiny hilltown of Civita di Bagnoregio.
See also this earlier Forum post about a Bolsena guidebook.