There are no volcanoes in Cuenca, Ecuador. Sangay volcano is the closest one, it is located in the Morona Santiago province, part of the Sangay National Reserve. The Sangay volcano is the least accessible and least studied volcano in Ecuador. Also, it is the most active volcano in Ecuador.
Although Sangay is the nearest mountain to Cuenca, if you are willing to travel a little north, El Altar and Chimborazo volcanoes are great tourist destinations. Mount Chimborazo is the highest point on Earth.