Europe is opening back up to Americans. Here's how to see some of its most iconic sites.

The door to European destinations keeps cracking open for Americans – and in some cases, has been wide open for weeks already. But even as coronavirus-era border restrictions continue to fall, travelers shouldn’t expect their trips to be anything like pre-pandemic visits.

“We’re thrilled that the E.U. is once again welcoming Americans, but ‘open’ does not mean ‘pre-Covid norms,’ and whatever rules exist today will undoubtedly continue to change in the days, weeks and months to come,” said Jennifer Tombaugh, president of guided tour and river cruise operator Tauck, in an email.

That word of warning especially applies to some of the continent’s most popular attractions, which are often overwhelmed with crowds even in normal times. With social distancing measures and reduced capacity, getting access to a favorite spot – especially in tight indoor spaces – could be more of a challenge than ever.

Tombaugh says travelers should do advance research for any spot they hope to visit, plan extra time and bring proof of vaccination if they are going to a place that requires it. She suggests working with a travel adviser or tour operator who will be keeping on top of local requirements.

Countries and attractions will be putting a major emphasis on safety and security, Luís Araújo, president of the European Travel Commission, said in a statement. He said travelers should check national tourism office websites, the Re-Open E.U. app or Visit Europe for information about rules from country to country. And visitors should check to see if advance reservations will be necessary at popular sites.

“However, with appropriate safeguards in place, we are confident that US travellers will be able to finally enjoy their favourite European destinations to the fullest,” he wrote in the statement.

Some of Europe’s most-visited attractions are open now, or reopening soon, with new restrictions that travelers should keep in mind. And while many countries like France, Italy, Spain and Greece are open to U.S. travelers with some restrictions, others like England still require Americans to quarantine upon arrival.

The Louvre

The famed museum in Paris is requiring everyone, even people who qualify for free admission, to book a time slot for their visit. Payments at the museum can be made only by card.

Masks are required for anyone older than 11 and will not be provided by the museum. Visitors have to use the hand sanitizer dispenser before walking inside, and they must adhere to social distancing rules.

Restaurants and cafes are closed, but certain outdoor catering facilities are open. Some rooms are temporarily closed, and the Salle des États – where the Mona Lisa is on display – has separate doors for entry and exit.

Eiffel Tower

The iconic attraction in Paris reopens July 16, with advance tickets already on sale – and the earliest reopening dates low on availability. Face masks and physical distancing will be required.

Buckingham Palace

The British royal residences have put advance booking and timed ticketing into place and reduced the number of people who can visit. A long list of safety measures is available online.

Face coverings are required in indoor spaces and security checks, but not in outdoor areas. They can be removed once seated at a table in cafes.

Some areas, like the Royal Mews at the palace, are temporarily closed to the public.

Stonehenge

The monument in England is limiting visitor numbers and requiring advance booking, even for those who can access free tickets. Face coverings are required indoors, including on shuttle buses. Visitors must bring their own. Some parts of sites might be closed, and some might have different routes than usual to follow.

Sagrada Familia

Visitors to the basilica in Barcelona can only buy tickets online. Everyone must wear a mask and keep a distance of six feet from others. People are asked not to bring bags to speed up the security process. Some spaces where distancing is not possible will remain closed.

The Acropolis

Visitors to the archaeological site in Athens need to keep about four and a half feet apart. The maximum number of visitors allowed in a group is 20, unless members belong to the same family. Masks are required for those 4 and older.

Colosseum

Reservations are required, and some areas at the ancient site in Rome are off limits. Masks are required, and visitors’ temperatures will be taken at the entrance. Everyone has to keep a distance of three feet.

Vatican Museum

The Vatican Museums, including the Sistine Chapel, require advance bookings with specific entry times. Entry is phased in 30-minute intervals, and if someone shows up late, they won’t be allowed in and won’t be able to get a refund.

Face coverings are required for entry to the Vatican Museums and Gardens, and everyone must have their temperature checked. Visitors need to avoid gatherings and keep a distance of more than three feet from others.