As more borders reopen and flight service resumes, the U.S. State Department lifted its Level 4 advisory against international travel on Thursday. Nonetheless, the U.S. remains one of the hardest-hit countries amid the COVID-19 pandemic and thus Americans are still limited in terms of available international destinations this summer. While many have strict requirements and other obstacles in place, here are 20 countries U.S. travelers can visit right now.

Antigua and Barbuda reopened to tourism earlier this summer, however, all travelers arriving by air must have a negative COVID-19 PCR (nasal swab) test result produced within seven days of their flight (children under age 12 are exempt). What's more, travelers will be monitored for COVID-19 for periods of up to 14 days, the Caribbean destination warns, adding that visitors "may be required to undergo further testing for COVID-19 on arrival or at the hotel or place of lodging as determined by the Health Authorities."

Aruba opened to Americans on July 10, requiring visitors from at least 24 states to provide proof of a negative PCR test result within 72 hours of their departure. Travelers in other states have the option of getting tested within three days of their visit or upon arrival at the airport but also at their own expense. The island is also requiring travelers to purchase "Aruba Visitors Insurance" to protect themselves in the event that they contract coronavirus on their trip.

Following a brief ban last month, Americans can once again visit the Bahamas but the requirements are unsurprisingly strict as U.S. travelers will need to quarantine for at least 14 days upon arrival in addition to uploading a negative COVID-19 PCR test result with their Bahamas Health Visa application. The Bahamas is also among the Caribbean destinations that the U.S. State Department is encouraging Americans to avoid due to the pandemic.

Barbados is open to U.S. travelers who can show proof of a negative PCR test result obtained within 72 hours of departure. Visitors will be asked various health questions and be required to complete an online immigration card prior to their trip.

Americans eyeing a vacation in Bermuda will need to complete the Bermuda travel authorization process online, which includes a $75 fee per traveler to cover COVID-19 testing in Bermuda. Visitors will also need proof of a negative PCR test result taken no more than seven days before departure.

Cambodia reopened to international travel in June but the requirements to visit are as stiff as they come. The Southeast Asian destination is requiring travelers to put down a $3,000 deposit to cover COVID-19-related expenses, including a test upon arrival and have at least $50,000 worth of travel insurance for potential quarantine housing and medical treatment.

While Americans remain banned from visiting much of Europe this summer, Croatia began hosting foreign nationals, including U.S. citizens, for business, tourism, education and other reasons on July 10. Visitors must present a negative PCR test result not older than 48 hours to avoid potential quarantine.

Dominica began welcoming back tourists on August 7. Eligible visitors must obtain a negative COVID-19 test result produced 24 to 72 hours prior to arrival and complete an online questionnaire at least 24 hours in advance. Rapid test screening and other health checks will be conducted on arrival.

The Dominican Republic reopened to international tourism with few requirements on July 1 but is now requiring visitors to undergo COVID-19 testing upon arrival at the airport if they aren't able to provide evidence of a negative PCR test result recorded within five days of their arrival. The DR remains the heaviest-hit destination in the Caribbean and the State Department is advising Americans to avoid travel to the country for the time being.

Egypt began easing travel restrictions on July 1, reopening some resorts and popular sites with enhanced cleaning and screening measures in place.

Visiting the Islands of Tahiti and Bora Bora will undoubtedly be more complicated in the time of coronavirus but Americans are welcome to do so as long as they are willing to undergo PCR testing, provide proof of travel insurance and follow the destination's other important health and safety protocols.

Jamaica is yet another Caribbean destination currently open to Americans. However, travelers coming from heavily-impacted states such as Arizona, Florida, New York and Texas are required to upload a negative PCR test result taken within 10 days of travel. Still, all visitors must complete the country's online travel authorization and still face the possibility of undergoing screening and potential testing on arrival.

The Maldives is one of the most relaxed international destinations that Americans can visit right now. The small island nation is requiring that visitors complete a health declaration upon arrival and book their accommodations in advance of their trip but otherwise isn't requiring travelers to provide proof of a negative test result.

Mexico remains one of the most accessible international destinations for Americans this summer. Flights are operating between the two countries and visitors do not require a negative COVID-19 test result to gain entry. U.S. travelers should still anticipate elevated screening including temperature checks upon arrival at airports and hotels.

Rwanda reopened to commercial flights on August 1, requiring international visitors to present proof of a negative PCR test result taken within 72 hours of arrival. However, access to the country's top sites will require an additional negative test upon landing at the airport.

St. Barts is giving Americans the green light to visit if they can show a negative PCR test result that was taken within 72 hours of arrival. Visitors staying longer than one week should expect to pay for additional COVID-19 testing.

Americans are welcome in Saint Lucia but the island is requiring that all visitors produce a negative PCR test result taken no more than seven days before arrival. Travelers must also complete a Pre-Arrival Travel Registration Form and have confirmed reservations at a COVID-19 certified accommodation.

Visitors to St. Vincent and the Grenadines can bypass the required PCR test upon arrival if they have proof of a negative PCR test within two days of travel or a negative antibody test result produced within five days of arrival. Other requirements include the completion of the "VINCYCOVID questionnaire" and "VINCYCOVID App*Approval."

Turkey began welcoming back tourists nearly two months ago, requiring that arrivals complete a form providing additional information on their health and travel history and undergo screening for COVID-19 symptoms.

Turks and Caicos is inviting Americans to visit but they'll first need to obtain certification through the TCI Assured Portal, which will require them to submit a negative PCR test result taken within five days of arrival (children under the age of 10 are exempt), proof of insurance covering COVID-19 medical costs and full hospitalization, doctors' visits, prescriptions and air ambulance as well as a completed online health screening questionnaire.