If you are looking for fun, Uruguay is fun from late December to early February (the peak of the summer). The rest of the time, Uruguay is a small, nice country with nice people. Probably colder than you expected.
The fun part is in the east. Punta del este is, if you are loaded, compared to Miami sometimes. Nice beaches, lots of clubs, expensive hotels and casinos. Music at the beach, djs and drinks everywhere. It all costs at least x1.5 more than the rest of the country. Lots of exclusive stuff there.
If you are not loaded, or at least want some fun in a less flashy way, you have to head Rocha.
La Paloma(in Rocha) , has nice beaches as well, is more like surf oriented, plenty of places to camp, and lots of clubs at night close to the beach.
Punta del Diablo(Rocha as well) , is like 85% of the year, a fishers town, cold, mostly dead, few people and just a fistful of things to do.
In plain summer? Babyyyy, lots of people camping, lots of drinking, music, clubs, some hippie stuff as well, beaches crowded with smashed people from last night, music blasting, the whole thing.
Cabo Polonio (yes, Rocha) is like the final boss for hippies. Is a small town in the beach, far for from civilization, they literally have no electricity, with a few exceptions, is a fishers town as well, only reachable after hiking for like 5 kilometers of dunes, or in an all terrain bus that takes you there. You are not allowed to camp there, as it is not controlled by police, but controlled by the Marine. Only option is hostels, or a small cabin. Everything is reggae, everything is dreadlocks, weed, beer, fishing, selling handcrafted shit to everyone who is not from there, or is just there for the day, really popular among hippie tourist. To the point that some of those tourist are actually living there now.
The whole idea of not being commercial and away from people, turned it in a really expensive place to stay, so hostels are expensive.