We found out that the Rio de la Plata is the largest river in the world. I thought that the term "river" was probably just being interpreted loosely since it's said to be about 200km at its widest, but then realized that it's actually fresh water! So in Colonia del Sacramento, you've got this town that, on a map, appears to just be sitting on the Atlantic Ocean. But it's actually sitting on a giant river!
We also learned that those typical Spanish tiles (the red ones you see on the roofs of houses) were made by laying the clay over the thigh of the tilemaker. Their shape makes a lot more sense now!