This was an exellent hike which I did with some friends I met in Leon, Nicaragua (this written in Costa Rica). We did it without a guide and requires some navigation but you can find the GPX here. There are some arrows painted onto trees for half the hike but don´t follow them forever since they end up going south away from the volcano. An alternative descent is to continue straight down after the large mango tree instead of turning left back to San Jacinto. Relatively straight forward and brings you back on the main road closer to Leon.
This was one of the few times that I´ve actually seen lava (albeit a few hundred metres away in the centre of a very impressive crater). Do it.

Gabriel: from Canada, riding his motorbike to South America. Thomas: experienced skydiver with a few base jumps under his belt (i.e. BAMF) and his awesome wife Mary : good times.

Thomas and Mary didn´t bring a tent so this roof (that we didn´t know about) provided an an immensely fortunate shelter, especially since it rained hard for half an hour. Careful not to leave your kit for too long since the area is also shared by cows that loved eating our packs (and Gabriel´s hat). Cow saliva is tricky to remove.