personally, but the time we got to Cabo Polonio, we had seen loads of sea lions. we had sat with them on the beach at Punta Norte at Peninsuala Valdes, and we had seen them while whale watching in Puerto Piramides...so, seeing this very large sea lion colony wasn't all that impressive...but, if you haven't had your fill of sealions, it really would be...
the faro (or lighthouse) is the only place on Cabo Polonio that has electricty. It's in a really lovely spot...and you won't be able to miss it.
the dunes are really quite something....you can climb (the sand is, surprising, quite easy to walk on), and just marvel at being surrounded by all that sand...
I stayed in the nearby village of Valizas and walked the 6-7 km (2 hours) to Cabo Polonio. We walked over the sand dunes on the way out and along the beach on the way back.
The walk was very nice. Great views from start when I climbed the sand dunes, later we saw the odd sight of cows grassing next to beach.
All along we didn't meet anybody, so it was a very peaceful walk.
Cabo Polonio is situated at a bay and there is a lighthouse you can climb to get a nice overview of the small houses scattered around between the rocks.