- 50plus Expeditions
 - Adventure travel for people over 50 featuring active, off-the-beaten-path, small group tours around the globe. - 1st Sports Tours
- Offering international sports tours for soccer, hockey, baseball, basketball, golf, and rugby.
- 1-World Adventures
- Directory of luxury and adventure travel operators.
- 1st Class Adventure Vacations
- Source for hiking, biking, fishing, paddling, wildlife, and other outdoor adventures.
- 1+1 Ranch
- Working quarter horse and cattle ranch offering riding, ranch experience, and private four bedroom guest house.
- 20th Century Railroad Club
- Offers volunteer activities for rail enthusiasts, as well as rail travel opportunities in the U.S. for families, singles, and groups.
- 206 Tours
- Offers Catholic pilgrimages to Europe, the Holy Land, Venezuela, and Mexico.
- 2Afrika
- Specializing in tours to South Africa including safaris.
- 58° 22' North Sailing Charters
- Bareboat chartering on the glacier-filled fjords of Alaska.
 2000 Tours
- Offers bus tours and packages to concerts, sporting events, theatre, and more, from London, Ontario.- 4Winds Tours
- Offers cycling, barging, spring flower, and brewery tours in Holland and France as well as hiking/biking tours in Austria, Ireland, and Denmark.
- 6 Passengers, The
- Offers trips in Rangiroa.
- 4* & 5* South America Travel
- Offering escorted tours and custom group, agricultural, and incentive travel to Argentina, Brazil, Chile, and Peru, including Patagonia and the Amazon.
- 6 Wheeler Bushmobile
- Offers 1-9 day trips throughout Australia.
- 4**** South America Travel: Brazil
- Escorted tours and vacations to Brazil including group discounts, incentive, and custom tours.
- 100GoGo World Scientific Expedition Network
- Dedicated to academic scientific expeditions and world scientist community. Also includes a list of future field trips and articles, journals, and photos of the past expeditions.
- 3rd Eye Travel
- Offers ecologically and culturally sensitive tours of the hilltribe villages in Thailand.
- 707 Travel Services
- Provides coach tours and daily bus services for overseas visitors in Singapore and Malaysia.
- 4x4 Africa Tours
- Offering 4x4 adventure tours in South Africa, Zambia, Mozambique, and Namibia.
- 85th Street Traveler
- Pat and Joe Wolfe lead tours to Kenya, Russia, Yellowstone, and the Rose Bowl Parade, plus arrange specialized travel for individuals and groups.
- 1-800-Charter.com
- Offers bus charter reservations for the U.S. and Canada.
- 30x60 Adventure Series
- Offering adventure travel services to Argentina.
- 4 and 5 star South America Travel: Chile
- 4- and 5-star tours and custom travel vacations to the wonders of Chile: Patagonia cruises, Andes mountains, Atacama desert, Santiago and Chilean wine tours.
- 360 Student Travel
- Summer community service, language immersion, adventure, and pre-college enrichment programs for teenagers. Destinations throughout the world.
- 30,000 Island Cruise Lines
- 4 Walls & A Bed
- Offers hotel rooms to fans attending NASCAR races in Daytona, Bristol, Talladega, and Dover.
- 4th Summit Mount Kilimanjaro
- Climb Mount Kilimanjaro in Tanzania, the tallest mountain in Africa with 4th Summit. Organizes private climbs, set departures and charity climbs on the Machame, Shira, Umbwe, and Lemosho routes.
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