Lake Titicaca is the highest navigable lake in the world. You can visit it from Peru or Bolivia, but if you got to pick one, go for the Bolivian side. It will be reasonably cheaper and much less crowded.
The real Copa Cabana
Funny fact: the small town of Copacabana is actually the origin of the name of the most famous Brazilian beach Copacabana in Brazil. There are many stories, but the one that comes up most is that of a monk travelling by boat and arriving at the beach named it after the patron saint of Bolivia, being Our Lady of Copacabana.
The town of Copacabana has not much to offer, but it has an amazing basilic (for Our Lady of Copacabana) that is wort the visit. Most importantly is that from Copacabana you can take a 2h boat to the little island Isla Del Sol.
Make sure they drop you of at the north of the island, where you can start your hike down to the south. Also make sure to stay at least one night (accommodation is plenty in the south) on the island so can witness the amazing sunset from one of the many lookouts.
And if you are brave enough, we recommend you to go to the very north of the island, past the table ruin, to this magical pier at one of the many little beaches and go for a swim! The water is cold, but so pure. Definitely worth to get wet. Oh and while you're there, you ll have to opportunity to take these breath taking photos ! Oh, and make sure to watch the video of our hike, down at the bottom of this post)