The main reason to go to Guatemala was to see Vulcano de Fuego. It's quite active one - eruption went each 5 to 10 minutes and was amazing at night.
It was a bit exhausting to make trekking from 1800 to 3600 meters above sea level in 4 hours, but we've made it. And stayed there for 2 nights. We had to hire porters to bring all the water, tent and equipment needed with us.