Whereas the Internet said it was possible to climb Volcan Concepcion in Nicaragua and it was just the tour guides that said it wasn't, the internet and the local tour guides firmly agree that it is not possible to climb Volcan Arenal in Costa Rica because it's too dangerous. Arenal spurts large lava rocks and poisonous gases into the air on a daily basis. Hikers have apparently died several times in the last few years after ignoring the warnings and trying to climb the volcano. Heeding the warnings, I reluctantly opted for an overpriced guided tour with Carlos the Mexican, a night hike to a safe distance away from the base of the volcano to hopefully see red hot lava in the dark.
Hopefully was always going to be the key word. There is always an element of luck in seeing a volcano amongst the cloud cover, as I myself found a few days earlier on Volcan Concepcion in Nicaragua. Some tourists apparently don't see Arenal during several day vacations in Costa Rica, but I was lucky to see an exploding cloud of poisonous gases, showers of lava rocks rolling down the side of the volcano, and just before the overpriced tour finished and we got the minibus back to our hotel, a small eruption of red hot lava into the night sky.
This is good photography (that I did not take) of Volcan Arenal erupting lava at night
This is bad photography (that I did take) of Volcan Arenal erupting lava at night