Try an indigenous type of steam-bath known as a temazcal. Sit in a small building with heats that go up to 49°C and then either be covered in towels or dunked into cold water.
This is the location of the famous Mexican Pipeline, with several international surfing competitions being held here annually. This beach is only for expert surfers and very strong swimmers; even experienced surfers have been injured here, and many people have drowned. The southern end of the beach near Punta Zicatela has consistently good waves. If you don't surf, you should at least make it over to the beach restaurant Los Tios and have a beer on the beach while you watch people surfing in the sunset. This is also a good place from which to watch over breakfast when there's a surf competition on.
The most scenic and safest beach for swimming is Playa Carrizalillo. Take a taxi unless you want a half-hour walk. Carrizalillo is small, gorgeous, and not too crowded, 167 steps from street level down to the beach (then back up again). There are some surfers and some boats, but mainly swimmers enjoying the waves. This is a good beach for swimming or learning surfing with few restaurants.
A good, pleasant beach for swimming, with a few beachside restaurants with loungers. Visitors can use the loungers for free provided they purchase a drink or food from the restaurant. The rocky area between this beach and neighboring Playa Puerto Angelito is probably the best place in town for snorkeling - sea turtles and stingrays can often be seen here.
This beach is good for swimming and boogie boarding, and very popular with locals.