Photo: Huguitoportal, CC BY-SA 3.0 via Wikimedia Commons
Small brick ruin between the lighthouse and the main square. You would not know what kind of building it was if there weren't a sign next to it.
© OpenStreetMap contributors
For a nominal fee you can go up to the top of the lighthouse (faro) and see most of the city and look out over the city and Rio de la Plata. On a clear day probably even Buenos Aires is visible. The lighthouse was built in 1857 and it is 26.92 m high with 118 steps. Its light is not white but red.
Museo Naval
Casa de Nacarello
A Portuguese 18th-century building: an example of a furnished home from those times.
Museo Municipal Dr. Bautista Rebuffo
Museum in two floors presenting objects of daily life 200 years ago as well as the works of scientists and explorers that have lived and worked in the town. In the room dedicated to a biologist there are various two-, six-, and eight-legged creatures on display, as well as small and very large fossils. If you're lucky you get to meet the offspring hanging next to the fusebox in the back corner. This museum is also where you buy the U$50 ticket that allows you into all eight museums.
Casa del Virrey
Reconstructed somewhat on the ruins of the original building. Don't miss the whale skeleton on display just to the west of it!
Plaza Mayor
Everyone wandering around the barrio histórico will pass through the main square at some point. It is lined by several points of interest for travelers such as museums, places to eat, drink and sleep, and some small stands selling souvenirs. On the western edge there are old cannons laying on the ground and in the middle there is a palm functioning as an electrical pole and a lamp post complete with a fuse box and even electrical sockets! If you wonder about the noise from the palms, it's from small green parrots that have their nests there.