If you can get to Lake Titicaca, do so. It’s beautiful.
I unfortunately only scheduled a single day/night for the trip. Isla del Sol really requires at least 2 nights. There’s a *really* steep and exhausting hike right off of the docks at the south end of the island (and keep in mind, the lake is at 3,812 m (12,507 ft) elevation). I never did make it as far as the north end, which I regret.
Copacabana, on the mainland shore of the lake, is a cute little town but not worth too much time.
Casa de la Luna is brand new (was still partially under construction when I was there) but is an absolutely amazing and beautiful hotel.