The route out from La Paz to Copacabana on Lake Titicaca is an easy day trip and frequented by many travelers. But I want to give you even more reason to go by telling you about a few other things along the way that are just as lovely.
About halfway to Copacabana (and you can get here by train too) is Tiwanaku, a settlement comprised of several archaeological sites of historic Inca relics that even today are not entirely uncovered. There is an actual museum south of the little town where you can begin, and then walk among the various ruins around it, including Puma Punku, Akapana, the Temple and temple grounds of Kalasasaya, Puerta del Sol (the Sun Door) and the Puerta de la Luna (the Moon Door). I recommend you get here as early possible as it will be easy to run out of time!
Back on a bus, you'll then want to backtrack toward La Paz a bit, until you get to the town of Laja, which is worth a stop because the combination of its rustic stone church, plaza, and traditinally dressed people is as quintessential a scene of Bolivia as you will find.
Going north from Laja, when you get to the town of Batallas, instead of continuing north to Copacabana just yet, get off and take a short taxi ride out to idyllic lakeside village of Puerto Perez, which will treat you to a most authentic scene of how people of the lake have lived for centuries. It's beautiful and the real Lake Titicaca. Then get back to Batallas and get on another bus northward to Copacabana.
You will eventually come to the end of the road where the bus will board a ferry to cross a small strait of water, Estrecho de Tiquina, that will take you over to the peninsula that is shared with Peru, and on which is your destination of this route. The bus will wind you up the peninsula and along the way you'll get plenty of gorgeous scenes of Lake Titicaca surrounding it, until you at last wind into the beachside municipality of Copacabana, remininiscent of Greek islands but with a distinctive high Andean flair.
Now, it would be a huge waste of your time to come out to Copacabana without taking the further boat ride out to Isla del Sol (Sun Island), blessed with blue skies, diamond colored beaches, green valleys and trails, and so much more you could enjoy hikes there forever. Don't miss it!Kali