Copacabana and Lake Titikaka
Copacabana and Lake Titicaca are two of Bolivia's most valued landmarks. My fondest memory is skimming across the lake on a hydrofoil to Peru - about 6 hours. On the Island of the Sun you can get out and do some hiking and see some Incan ruins. The Island of the Moon is much smaller, but also pretty. Skip the pizza and have some Titicaca trout on the shore in Copa. It doesn't get fresher than water-to-grill. Skip Copacabana around February 2nd unless you're into hundreds of people dancing drunkenly in the streets and stay at the Andean Eco Village in Huatajata instead.