Famous for having been the last bastion of the native people before Spanish colonisation became total, the ruins of Quilmes are still in a good state of conservation. The site covers about 30 hectares and you can still see a large part of it.
I was particularly interested in its labyrinth like structure and by how spread out it is, which makes it easy to imagine the life of the people who lived there. Strolling around the ancient city is still the best way to explore it and I recommend you climb up to the two fortresses, not far from the summit of Cerro Alto de Ray, because from there you have a superb view over the whole of the site and the surrounding countryside.
I was also very interested in the archaeological museum. The many objects there help you to imagine the life of the inhabitants of Quilmes.