On the south shore of Lake Izabal, hot volcanic springs emerge directly into the lake water, creating warm patches where you can swim in mineral-rich water surrounded by jungle. The springs are accessible by boat from Río Dulce town or from the small community of El Estor to the west; most visitors combine them with a stop at the nearby waterfall.
The experience is low-key and genuinely off the beaten track. There are simple palapa restaurants on the shore serving fresh fish from the lake. Go in the morning before tour boats arrive and you may have the place almost to yourself.