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When it comes to relaxing vacations, cruises are hard to beat for value and convenience. They're the original all-inclusive holiday, since fares typically include stateroom, all meals, most shipboard activities and, sometimes, even shore excursions.

Taking a cruise is a convenient way to explore several destinations in one trip. You only unpack once, but visit a different port of call each day. What's more, ships can take you to some of the world's most exotic places, from Antarctica to the North Pole.

Cruising is so popular that vessels now ply virtually every waterway on the planet. In addition to long-popular itineraries in the Caribbean, Alaska and the Mediterranean, you can explore the Amazon River, China's mighty Yangtze River, the South Seas, the South American coast and, of course, the rivers of North America. Ships range from megaliners to upscale, yachtlike vessels to bare-bones research ships. There is so much variety that even people who never considered cruising can find a trip and a ship to suit their taste.

Options also run a gamut of prices, from three-day cruises to high-end journeys. And there are other ways to maximize the value:

*Reserve early. Many cruise lines offer early-booking discounts of up to 20 percent to entice passengers.

*Sail at the last minute. If you aren't too picky about where you go, take advantage of cruise lines' last-minute bargains to fill empty berths.

*Look for special offers. Free airfare (or deeply discounted air add-ons), pre- and post-cruise tour packages, two-for-one fares and repositioning cruises (when ships are moved from, say, Alaska in the summer to the Caribbean in the winter) make cruises an even better deal.

*Check out the shore excursions. Some cruise lines include shore excursions in the overall fare, especially for trips with an educational or adventurous theme. Others charge for escorted tours at ports of call. Cruise lines have become more creative with these excursions, offering a range from soft-adventure day trips to cultural forays.

*Pick a theme. From golf trips to wine-tasting to literature, there are a variety of special-interest cruises. These often include lectures, themed events, special shore excursions.

*Surf the Internet. Cruise lines post special offers and last-minute discounts on their Web sites. This is a great way to shop around, compare itineraries, check out ships, cuisine, activities and other amenities. The Cruise Lines Industry Association Web page at www.cruising.org has links to members' sites.

*Call your travel agent. Sure, you can find bargain fares on the Web, but a travel agent may do even better. Look for an agent with lots of experience booking cruises; agents often parlay their relationship with cruise lines to arrange special perks for customers.

Some ships dazzle passengers with luxurious surroundings and attentive service. Silversea Cruises pampers passengers with all-inclusive vacations that include round-trip airfare, deluxe pre-cruise hotel accommodations, shore excursions and everything they need aboard ship — right down to gratuities for the staff. Itineraries cruise the waters of the Mediterranean, South America, Amazon River, the Caribbean, New England, Africa and India. Silversea also has special golf and culinary trips, as well as the National Geographic series of adventures.

Radisson Seven Seas Cruises also tempt with high-end vessels and itineraries. There's the double-hull SSC Radisson Diamond, which has a superstable design ideal for those who have trouble finding their sea legs. The line's MS Paul Gauguin specializes in luxury itineraries to Polynesia. All staterooms on Radisson's new, 700-passenger Mariner will be suites with private balconies.

If you've always dreamed of sailing on a luxury yacht, book a trip aboard one of Windstar Cruises' 148-passenger sail ships. Spacious staterooms, excellent cuisine and uncrowded ports of call make Windstar's cruises to the Caribbean, Mediterranean and South Pacific favorites with cruisers who can afford to sail with any line.

For a full schedule of shipboard activities and every imaginable amenity, a megaliner is the way to go. Princess Cruises' newest ships, the Ocean Princess and Grand Princess, accommodate 1,900 and 2,600 passengers respectively. To keep that many people happy, ships boast dozens of restaurants and bars, a choice of pools, fitness and spa facilities, water sports and other activities.

If you like the ambiance of a liner, but don't want to share it with a lot of other passengers, check out Celebrity Cruises' ships. These recall the elegance of a bygone era of sea travel, combined, of course, with thoroughly modern amenities. Celebrity's fleet of seven ships hosts 300 to 825 passengers. The line's newest member, the Millennium, has a 25,000-square-foot AquaSpa facility, and one of its dining rooms boasts the wood panels from the RMS Olympic (sister ship of the Titanic).

If you believe in lifelong education, an educational cruise is ideal. These trips typically explore remote destinations in small vessels and are accompanied by expert naturalists, historians and special lecturers. Instead of docking at a busy cruise-ship port, passengers go ashore in sturdy Zodiac landing craft. Shore excursions are accompanied by interesting lectures and other presentations.

These journeys also are a good value, because shore excursions, lectures, shipboard meals and activities usually are included in the fare. Toronto-based Marine Expeditions offers cruises to Greenland and Northern Canada, the Galapagos Islands and Antarctica aboard vessels that host 100 to 128 passengers. Fares often include airfare from North America.

Clipper Cruise Lines' fleet of four ships accommodate 100 to 138 passengers for journeys to Mexico, Antarctica, Australia, New Zealand and closer to home, such as an autumn cruise on the Hudson River and Chesapeake Bay. Seattle-based Society Expeditions also offers cruises to Antarctica, the South Pacific, as well as an extensive choice of itineraries to Alaska and the Russian Far East. Also check out Linblad Expeditions, which covers the globe with land-cruise itineraries; special guests include the likes of Lech Walesa and Wally Schirra.