Some intransigent people are of the unwavering belief that a genuine day trip requires meticulous planning down to the last detail. For them a complete change in scenery from one's everyday surroundings is in order. We're a little more relaxed. A leisurely drive is nice. So is an alternate ambiance. But we aren't particularly enamored of rigid schedules. We prefer an unhurried, casual outing like Biscayne National Park's three-hour boat tour to Boca Chita Island, which is offered from January to April for a mere $19.95 plus tax ($9.95 for kids under ten years old). In the early afternoon, you and 47 other adventurers will zoom off in a glass-bottom boat to the 32-acre island. Owned by the wealthy Honeywell family from 1937 to 1945, it was recently listed on the National Register of Historic Places. Once you disembark a guide will chat about the history of the onetime playground for the moneyed set, that still includes ten structures built in the Thirties, coral-rock walls, and a cute but useless 65-foot coral-rock lighthouse. After all that structured activity, you're free to roam, snap photos, picnic, or just hang out. (If you dock your own boat on the key, you can camp overnight, but the facilities are rather austere.) After your brief, invigorating visit to a quieter place in time, you'll be ready to hop back into your car and return to hectic civilization.