On the Ecuadoran Andes, you can find the Quilotoa crater lake. As the name suggests, it is a water filled caldera and about 3km wide. It wsa formed by the collapse of the volcano following a catastrophic eruption about 600 years ago.
The eruption is estimated to have followed after a dormant period of 14,000 years and is known as the 1280 Plinian eruption.. The fourth (of seven) eruptive phase was phreatomagmatic, indicating that a Crater lake was already present at that time.
The lake is about 250m deep and is green in colour due to the dissolved minerals.
There is a hiking trail called Quilotoa loop. It is about a four day trek through some spectacular sceneries. I would highly recommend this loop – the finale is the lake so getting here and then seeing this beautiful natural wonder is a treat.