San Martin is a cozy little town. They have tours that go there daily. I would recommend renting your own car, as it comes out way cheaper and you get to run on your own schedule and stop off at the lakes you want to.
We headed out early morning with no traffic and we were able to make it within 2.5 hours. The town is small enough that you only need 3-4 hours to see it all unless you want to dine at a restaurant. Most places open at 10 or 11, so be mindful if you want to get there early.
There's really only 2 lakes that I think are worth stoping at, that have a big enough area to swim in or enjoy (although I forget the names) but the area is clearly visible.
It was really a quick trip for us to visit. I would recommend this outing if you have nothing else to visit, like to see lots of lakes (that you might not be willing to jump in) and like cozy small towns. The drive there is scenic as well, but can get a little redundant and it is winding. Great drive if you enjoy...driving.