It was too good to last.

While summer saw much of Europe open up to American visitors, offering them the chance to fulfill lockdown dreams of eating gelato in Italy or touring the art museums of Paris, the season's end has brought with it new restrictions, and the doors to the continent begin to close.

Earlier in September the European Union recommended that US visitors should be banned from nonessential travel to its member states due to rising Covid-19 cases in the States.

The news has prompted various European countries to update travel restrictions for Americans, while some have prohibited entry to US travelers completely.

Unsurprisingly, the changes have prompted widespread confusion, particularly for those planning to travel to Europe in the coming months.

Here's a look at the tightened rules and what they mean for American travelers.

Can Americans still travel to Europe?

More countries may soon restrict access to Americans.
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Yes, they can. Only a small number of countries have so far restricted all nonessential arrivals from the United States. Since the EU advice was issued, Bulgaria, Norway and Sweden are the only ones to restrict all access.

However, while at least one destination -- Greece -- has ruled out imposing new curbs on travel in the near future, it's safe to say that Americans, particularly those who are unvaccinated, are likely to face more restrictions in the days and weeks to come.

What are the new EU rules?

The European Union has dropped the United States from its safe list and advised its member states to reconsider allowing US travelers to enter without an essential reason.

Its advice is non-binding, however. There's no pressure for countries to adopt this measure and they're free to ignore it if they choose.

That means there's no blanket rule covering the continent. Instead each destination country is at liberty to adopt or ignore the advice according to their own preferences.

Given how valued US visitors are to Europe's tourism economies, it's likely that any decision to restrict their arrival will be taken with considerable reluctance.

What do the EU rules mean for Americans traveling to Europe?

A lot more red tape, uncertainty and research, that's for sure.

Ultimately it means that traveling to European countries is likely to become harder for Americans in the weeks ahead, although not necessarily impossible.

As the rules change, it's up to individual travelers to check their eligibility to travel. Although airlines may also do checks before departure, they won't need to in order to sell tickets.

It's worth checking CNN Travel's Unlocking the World guides for up to date info where relevant or the US embassy in the country of destination. And then keep checking as the rules can change with just a couple of days' notice.

Some countries may keep their doors open, but tweak requirements such as pre-departure Covid tests, quarantine arrangements or proof of vaccination.

Which countries can Americans visit in Europe?

Croatia is still open to Americans.
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Austria, Belgium, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Poland, Portugal, Romania, Slovakia, Slovenia and Spain are currently all open to fully vaccinated Americans.

The restrictions in place vary from country to country. Many destinations require travelers to submit a negative Covid test on arrival, while some have both testing and quarantine measures in place for vaccinated visitors.

France currently has no travel restrictions for fully vaccinated Americans, but a negative Covid test taken no more than 72 hours before arrival is required before they can enter Italy. A mandatory 10-day quarantine is set for fully vaccinated US travelers visiting the Netherlands, while those entering Germany must provide a negative Covid test result before being permitted to enter.

Fully vaccinated Americans are allowed to visit the United Kingdom, as well as Iceland, Liechtenstein and Switzerland.

However different testing and/or quarantine measures have been implemented in each country.

Is travel to Europe safe?

No travel during the pandemic is entirely Covid-risk free, even for vaccinated travelers, and the best way to stay safe is to remain at home and minimize exposure to the virus.

That said, if safety protocols like mask wearing, social distancing and hand sanitizing are adhered to, there's no reason why travelers can't have a safe trip to Europe. Statistically, most western European countries have lower Covid rates than the United States.

There are still Covid hotspots -- Montenegro recently experienced a major spike in cases -- so it's worth checking US Embassy travel advice at the destination. Again, it's a matter of research.

Are more countries going to close their borders?

It's not entirely clear. Since several European countries have introduced new restrictions for US travelers based on the EU's advice, it's possible that others will follow suit in the coming weeks.

The restrictions have come about because of the spread of Covid's Delta variant in the United States, with cases reaching their highest numbers in many months throughout July and August. As numbers remain high in September, and colder months expected to fuel the disease's spread, more restrictions seem likely.

What should I do if I've booked a trip to Europe?

If you've booked travel to a country that remains open to Americans, you shouldn't encounter any problems provided you follow all of the recommended advice.

But if the rules have changed since you booked, many hotels and airlines recognize the problems with Covid and restrictions and may offer refunds if you've booked directly. It's worth asking.

As with all travel during the pandemic, there is however a risk that you may wind up out of pocket.

Luis Araujo, President of the European Travel Commission, a nonprofit that promotes tourism in the continent, stresses that US travelers are still a huge priority for Europe despite the rule changes.

"American travelers are crucially important for Europe, and most European destinations are still open to US visitors and eager to welcome them back to our shores," Araujo tells CNN Travel in a statement.

"That said, we must accept that we are still living through the reality of this ongoing pandemic and will experience some setbacks on our way to recovery.

"Travelers from the US still have to be conscious of health measures and respect rules at their destination."

Should I book any future travel to Europe?

As mentioned above, with any travel plans in the current pandemic, there are risks they may have to be changed or canceled. If you're looking for an escape entirely free of bureaucratic hassle, uncertainty and stress, then perhaps the answer is a straightforward no.

But Araujo insists US citizens should "continue planning their trips to Europe," while keeping "an eye on all the latest travel rules and cancellation policies."

He adds: "Travelers are best advised to check the Reopen EU website and the websites of national tourism offices, which contain all information and safety requirements that are being regularly updated, including information on testing, passenger locator forms, as well as any other health measures in place.

"With current vaccination rates and safety protocols in place, safe international travel is absolutely possible, with this summer season proving that."

Which European countries have banned unvaccinated US travelers?

The Netherlands now requires vaccinated Americans to quarantine.
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Denmark, Finland, France, Latvia, Malta, Netherlands, and Spain have all banned nonessential unvaccinated US travelers. Meanwhile, all nonessential American travelers are prohibited from visiting Bulgaria, Norway and Sweden, regardless of their vaccination status.

Which vaccinations are accepted in Europe?

To be considered as a fully vaccinated visitor, travelers must have been administered with a complete dose of the vaccines approved by the European Medicines Agency (EMA) -- Pfizer, Moderna, AstraZeneca, and Janssen -- two weeks before their trip.

Can I travel to Europe with unvaccinated kids?

The new rules will not impact children who are too young to be vaccinated. Those under 12 can travel with vaccinated adults to European countries where US travelers are permitted to enter. But while under 12s are exempt from all restrictions in some countries, others require a negative Covid test.

Those aged between 12 and 18 are subject to the same rules and restrictions as adult travelers. Again, it's worth double-checking for each destination in case variations on these guidelines are introduced.