BELIZE CITY, Belize- It was just three words, the Great Blue Hole, that stuck in my head. A giant marine sinkhole in the center of Lighthouse Reef, 40 miles off the coast of Belize, the 407-foot-deep hole was such a mystery that ocean scientist Jacques Cousteau led an exploratory expedition to the site in 1971, and filmed the adventure. Which I'd forgotten. Until last summer, that is, when my wife Val and I decided to celebrate the lull in the Corona-virus lockdown with a brief vacation, one we agreed had to be outdoors, on a mountain trail, or alternatively, in the water.