Tunnel entrance near the Hidalgo Market, Guanajuato. The city sits in a bowl surrounded by steep hills. As a consequence, flooding had been a serious problem through most of the city’s history. In the late 18th C two major floods nearly wiped out the city. This spurred construction of large tunnels to divert floodwaters during the rainy season. These eventually crisscrossed a large part of the city. The flooding was eventually brought under control through means other than the tunnels, and many of the tunnels were converted into underground roadways. As a result, the streets of Guanajuato have very little traffic, as you can see in this photo.