It's a very popular trekking spot in Uruguay, there are a couple of different walks to choose from. The one we did was to make it to the top of the hill, which is about a two to three hour walk, but there is also another one called "El cañadon de los espejos". The last one is named after pools of rainwater with small waterfalls you arrive to when you reach to the end of the path. The place is said to be very beautiful after rainy days with the waterfalls in their full glamour.
There used to be a third walk to the "pozos azules" (or blue pools) which is now closed, and there is also a whole discussion about which ones are the true legendary blue pools which I won't go into.
La Sierra de las Animas is also very popular among mountain bikers who carry their bikes to the top and then slide from there.
Once we arrived to the place we payed the 40 uruguayan pesos fee, and listened carefully to the pleasetakegoodcareofthepark fifteen minutes lecture. The place is maintained as an ecological park and we learned that it's forbidden even to spit fruit seeds while walking in order to protect the original flora (killing anything that walks or crawls or flies is of course out of the question).
When you are on the top of the hill you understand why they used to call it Mirador Nacional (National watcher...err, no.. watchpost, sightseer...err, something like that) as you can see a great part of Maldonado and even Montevideo or so they say in clear days.
We crossed a bunch of horses on the way to the top, and one snake and one impressive tarantula on the way down.
If you are the kind of person that likes walking, watching nature and just talking with someone in the way to the top (to the peak) you probably would've enjoyed it.