Countries and areas where a visa is required.
Abkhazia
Afghanistan
Algeria
Angola
Artsakh
Australia - Electronic Travel Authority
Bangladesh
Bhutan
Bolivia
Brazil
Burkina Faso
Burundi
Cameroon
Cape Verde
Chad
China
Comoros
Democratic Republic of the Congo
Republic of the Congo
Crimea
Cuba
Djibouti
Eritrea
Gambia
Ghana
Guinea
[China] Hainan
Iran
Iraq
Iraqi Kurdistan
Jordan
Laos
Lebanon
Liberia
Libya
Madagascar
Malawi
Maldives
Mali
Margarita Island
Mauritania
Mozambique
Nauru
Nepal
Niger
Nigeria
Pakistan
Papua New Guinea
Paraguay
Principality of Sealand
Russia
Saudi Arabia
Sierra Leone
Somalia
Somaliland
South Sudan
Sudan
Syria
Tajikistan
Tanzania
Timor-Leste
Togo
Tonga
Turkmenistan
Tuvalu
United Arab Emirates
Uzbekistan
Venezuela
Yemen
Countries that require an E-visa
Azerbaijan
Bahrain
Benin
Cambodia
Côte d'Ivoire
Egypt
Ethiopia
Gabon
Guinea-Bissau
India
Kenya
Kuwait
Myanmar
Oman
Qatar
Rwanda
Sri Lanka
Turkey
Uganda
Vietnam
Zambia
Zimbabwe
Some countries will ask for just a passport and some like Australia require a visa. Most of the time your travel counselor will take care of setting you up with the visa if it is needed, but make sure that you ask, just to make sure. However if you are planning your own trip, it is very important that you check this out, as you will not be allowed on the plane without one if it is required.
The following is a list of countries and their requirements to enter them. However, as the world is constantly changing, it is best if you check out your courntry's government travel page to make sure you have everything you need. For the USA, it is United States Department of State at https://www.state.gov/travel/.
Countries or areas that require a Visitor's or Entry Permit, Tourist Card or other permit
Antarctica - Special permits required
Ascension Island - Entry Permit required
Ashmore and Cartier Islands - Special authorisation required
ATO zone - Special permission required
Baikonur & Priozersk - Special permission required
British Indian Ocean Territory - Special permit required
Clipperton Island - Special permit required
Closed cities of Russia - Special authorization required
Donetsk People's Republic - Restricted area
Eritrea outside Asmara - Travel permit required
Fiji - Visitor's Permit
Galápagos - Pre-registration required
Gorno-Badakhshan Autonomous Province - OIVR permit required
India PAP/RAP - PAP/RAP required
Jan Mayen - Permit required
Lau Province - Special permission required
Maldives outside Malé - Permission required
Mecca and Medina - Special access required
Mount Athos - Special permit required
Saint Helena - Visitor's Pass required
Samoa - Entry Permit
San Andrés and Leticia - Tourist Card on arrival
Seychelles - Visitor's Permit
Solomon Islands - Visitor's permit
South Georgia and the South Sandwich Islands - Permit required
Sudan outside Khartoum - Travel permit required
Sudan Darfur - Travel permit required
Suriname - Tourist Card
Tibet Autonomous Region - TTP required
Tristan da Cunha - Permission required
Tokelau - Entry permit required
UN Buffer Zone in Cyprus - Access Permit required
United States Minor Outlying Islands - Special permits required
Yemen outside Sana’a or Aden - Special permission required