El Zanjón is an experience you dont want to miss. Start in a 175 year old Mansion that leads to a series of underground tunnels left over from the city's earl settlement days way back in 1536. Tourists can take an hour long tour through the underground channelings of the city and enjoy a piece of history that not many have been able to partake in. el Zanjón is now considered a museum as an archeologist had to be called in when they first started to excavate the tunnels in San Telmo. El Zanjón is filled with colonial and post colonial artifacts including a brick tunnel that once served as a channeled tributary to the Rio de la Plata.