A full-on tourist day: we walked to the base of the volcano, amidst lizards, spiders and trees that had been blown over by volcanic rocks hurled from Arenal. Travelling with a Tour Guide has its advantages: not only did we get a cheap (and rather nice) hotel room, but we also saved ourselves $6 a piece by getting into the National Park for free. Bargain.
After that we went to a Cataratas with a pool, and a powerful flow of water that means that all the tourists stay firmly clung to the edge, for fear of undercurrents. We lounged and bathed in the accompanying, slightly tamer pool, that has a powerful throughflow of water nonetheless (great fun to wedge yourself in some rocks and feel the torrent flow past you).
After a slightly worrying, but non-existent engine problem (the drip turned out to be from the Air Conditioning) and dinner, we finished the evening in the Hot Springs - with pools heated up by the volcano (some too hot to even put your toe in, as I verified) and, best of all, a swim-up bar. I felt like I was in Magnum PI.