My first encounter with an octopus was during a night dive at Commercial Pier near Fort Lauderdale while lobster hunting. We were pretty close to the pier, and I turned my light to point under a coral head. It was already sliding into a crevasse before I realized what it was. It turned really blue for a second and pretty much dissappeared. My dive partner tried to lure him out, but to no avail.
Years later, I was having really fantastic dive in a reef pass around Rarotonga. It was pretty close to sunset, so some of the noturnal creatures were venturing forth. I saw a least a dozen lionfish, a couple of crabs, and a white tip reef shark. I was heading back to the beach, thinking to myself "The only thing that could make this any better would be to see an octopus." Not twenty feet later, I saw one slinking into a hole in the top of a coral. He seemed pretty pissed when I was hovering over his hole, so I left him alone pretty quickly. Two minutes later I saw another one!! That was one of the best dives of my life so far.