Adventures Are Just Starting With New Routes : Vietnam and South Africa are among the formerly restricted areas now open to passengers.

With the Cold War thawed and even Cuba a potential port of call in the next year or two, once-forbidden destinations are opening up all over the globe for adventurous cruise ships.

The 134-passenger Caledonian Star, of Connecticut-based Salen Lindblad Cruising, became the first to offer cruises to Vietnam last month, announcing them only three days after the U.S. Treasury Department relaxed a trade embargo in December.

Another company, Pearl Cruises, is offering three Vietnam cruises this year. The first two, marketed exclusively in Europe, have sold out, but the third, newly announced, departs July 11.

The 17-day program includes three days in Hong Kong before cruising along the Vietnamese coast to Haiphong (for Hanoi), Da Nang, Ho Chi Minh City and Nha Trang. Passengers disembark in Manila for a two-night hotel stay at the end of the cruise. Prices begin at $2,495 per person, double occupancy; add-on air fares are available.

Vietnam is not the only pioneering destination for expedition veteran Salen Lindblad. The line operated the first passenger ship in history to successfully transit the Northwest Passage across Canada’s High Arctic in 1984, and the first cruise to the North Pole aboard the Russian nuclear-powered icebreaker Sovetskiy Soyuz last year. The 96-passenger icebreaker also made the first-ever east-to-west passenger transit through Siberia’s Northeast Passage.

Both icebreaker cruises will be offered again this year by Salen Lindblad and Quark Expeditions, creator of the voyages. The transpolar expedition across the Arctic Ocean will leave from Provideniya, Siberia, Aug. 18 and arrive in Novaya Zemlya Sept. 9. This year’s Northeast Passage itinerary, the first-ever passenger transit from west to east, begins July 21 in Murmansk and ends Aug. 11 in Provideniya, with a charter flight to Anchorage. Prices for each range from $18,500 to $26,000 per person, double occupancy, a bit lower than the 1991 prices.

We were aboard the Caledonian Star at the end of November when it sailed into Cape Town on the first cruise to South Africa marketed in the United States after economic sanctions were lifted.

Among the ports of call in West and Southern Africa were first-ever cruise ship calls at the tiny island of Principe, half of the two-island nation of Sao Tome & Principe off the coast of Equatorial Guinea, and Alexander Bay, South Africa, famous for its vast diamond mines.

Now Salen Lindblad has announced that both the Caledonian Star and the highly lauded Frontier Spirit, an environment-friendly expedition ship built in 1990, will be operated under a new cruise banner. Ft. Lauderdale-based SeaQuest Cruises Limited opened its headquarters Feb. 3.

While not as new and elegant as the Frontier Spirit, the Caledonian Star, formerly the North Star from now-defunct Exploration Cruise Lines, is much more handsome than the other expedition vessels presently in service. A spacious and comfortable main lounge, with bar and piano for cocktail and after-dinner music, is supplemented by an attractive lecture room that doubles as a library and is the venue for lectures, films and slide shows. Coffee, tea and a tin of Danish cookies are always available for passengers to help themselves.

Two single cabins are available as well as double cabins and small suites. Prices range from about $211 to $388 a day per person, double occupancy, with singles costing about $355 a day. Closet and drawer space is limited. All bathrooms have showers only.

Chef Thomas Bertels, from Germany, is assisted by a team of Swedish chefs; cabin and dining stewards are Filipino. While the food is not haute cuisine , it is well prepared and varied, with expansive breakfast and lunch buffets as well as a la carte hot dishes cooked to order. The Swedish baker prepares fresh breads, pastries and cakes daily. Passengers may sit where they wish at the single-seating meals.

The Caledonian Star will return to South Africa in December with a 13-day cruise leaving Madagascar Dec. 6. The ship will call at Ile Juan de Nova, Morondava and Tulear in Madagascar, and in Durban, East London and Port Elizabeth, South Africa, before arriving in Cape Town for disembarkation.

To obtain brochures for any of these cruises, ask a travel agent or call Salen Lindblad at (800) 223-5688, SeaQuest at (800) 854-8999, Ocean Cruise Lines at (800) 556-8850 and/or Pearl Cruises at (800) 426-3588.