Trips worth making, by value
Patzcuaro is the natural base for the whole Purepecha lake region, and the day trips are honestly better than a second day in the town itself. Here they are ranked by what you actually get.
The lakeshore villages: Tzintzuntzan, Santa Fe de la Laguna, Ihuatzio
Travel: about 20 to 40 minutes around the lake by car or colectivo (approximate). What you do: This ring is the best half-day out and where the living craft culture actually is. Tzintzuntzan was the old Purepecha capital, with the Yacatas round-stepped pyramids on the hill above town, a former Franciscan convent with ancient olive trees, and a strong pottery and craft market. Santa Fe de la Laguna is the place for green-glazed clay cookware, bought straight from the makers. Ihuatzio has quieter, less-visited ruins. Go Sunday for the fullest village plazas. Verdict: Worth it, the top pick. Do this before Janitzio.
Santa Clara del Cobre
Travel: about 20 to 30 minutes south by car or colectivo (approximate). What you do: The copper town, where smiths still hammer sheet copper by hand into pots, plates and art. Watch a workshop, visit the small copper museum on the plaza, and buy directly at prices far below city shops. Verdict: Worth it. A rewarding, low-key half-day if you like crafts.
Janitzio island
Travel: a boat from the Patzcuaro pier, roughly 20 to 30 minutes each way (approximate). What you do: The famous outing, especially at Day of the Dead. You climb the steep, stall-lined lanes to the giant Morelos statue for the view back across the water. Verdict: Worth it once, with realistic expectations. The lake is degraded, the island is crowded, and the fishermen photo act is staged. Culturally interesting, not the postcard. Do the villages first.
Morelia
Travel: about 1 hour by bus or car (approximate). What you do: The state capital, with a huge pink-stone cathedral, a UNESCO colonial center, the aqueduct, and far bigger dining and nightlife than Patzcuaro. Easy as a full day, or your natural entry or exit point for the trip. Verdict: Worth it if you have the time. See Morelia.
Tzararacua falls and the Uruapan sierra
Travel: roughly 1 to 1.5 hours west toward Uruapan (approximate). What you do: Waterfalls, the national park in the middle of Uruapan, and avocado country. Verdict: Skip on a two-day visit. Only worth it if you are staying longer and specifically want nature; it is too far to pair well with the lake.
For how the colectivos and boats connect, see getting there and around, and remember the rule about daytime driving only on these rural roads, covered in is it safe.