Cruises to Explore Costa Rica Coast : Adventure tours include land excursions with naturalist guides to five national parks.

A series of adventure/nature cruises along the Pacific coast of Costa Rica will be offered this fall and winter by Temptress Cruises of Miami in cooperation with Grand Circle Travel, a Boston-based tour company that deals solely with the age-50-and-over market.

Voyagers on the six-night cruises will leave Puntarenas, Costa Rica’s major Pacific port, aboard the 174-foot, 62-passenger M.V. Temptress. It will visit five Costa Rican national parks--four of which are inaccessible by land.

All shore excursions are included in the fare. Passengers have their choice at each stop of taking either a “hard” or “soft” nature tour. Both tours are escorted by naturalists and differ mainly in the amount of strenuous activity, such as hiking in the humid rain forest.

The night before each stop, naturalists explain in detail what’s to be seen and what to expect on shore. In lieu of a tour, passengers may opt for free time on the beach, where snorkeling, water-skiing and sea kayaking are offered free. Scuba-diving and sportfishing are also available for a modest additional charge.

The Temptress, built in 1982, is air-conditioned, with all outside staterooms. It carries a Costa Rican crew and serves international cuisine, featuring daily offerings of fresh seafood, sometimes caught by passengers and crew.

There are two ways to book the cruises:

* Grand Circle offers a special all-inclusive package on selected sailings with an additional weeklong stay in a first-class hotel in Costa Rica’s capital, San Jose. Included are round-trip air fare from Miami to San Jose, half-day sightseeing in and around San Jose, daily breakfasts, transfers between San Jose and Puntarenas, and a Grand Circle host to help make free-time arrangements.

The packages are priced at $2,275 per person, double, for a Dec. 18 holiday cruise, and $1,995 per person for departures scheduled Jan. 8 and 29, Feb. 12 and 26, March 12 and April 9, 1993.

* On other dates, the six-night Temptress cruise is not limited to mature travelers, but offers the same type of hard/soft adventure option. Fare for regular Saturday-through-Friday cruises from Nov. 2 through May, 1993, is $1,495 from San Jose, not including air fare.

For more information, contact Grand Circle, 347 Congress St., Boston, Mass. 02210, (800) 248-3737; Temptress Cruises, 1600 N.W. Le Jeune Road, No. 301, Miami, Fla. 33126, (800) 336-8423, or check with your travel or cruise agent.