The summer beach houses have been booked for months. Rental car prices are through the roof — if you can even find one. National parks are as hot as ever. Much of the rest of the world is reopening slowly and with considerable hassle.

With 44 percent of adults in the United States fully vaccinated and more than 58 percent with at least one dose, the number of travelers is climbing in the country. According to a forecast released Tuesday, AAA expects more than 37 million people to travel over Memorial Day weekend — a sharp increase from last year that the group calls a “strong indicator for summer.”

“We are seeing many popular domestic destinations already selling out for the summer, especially national parks and beaches, due to pent-up demand for travel and many travelers opting to stay stateside,” Beth Washington, a travel adviser at the Virtuoso agency SmartFlyer, said in an email.

For those who haven’t started planning summer vacation, what is left to do?

Booking sites, destinations and other travel experts say one type of getaway is emerging for summer 2021 that wasn’t available last year because of coronavirus restrictions and safety fears: the big-city escape.

“If you are vaccinated and you want a room in midtown Manhattan to go and visit the MoMA or want to see the Lincoln Memorial, this summer might be the summer for you,” Brian Hoyt, spokesman for TripAdvisor, said in an email.

Metropolitan centers such as New York City, Chicago, Los Angeles and D.C. — once buttoned up tight against travel — are targeting tourists with advertising campaigns, reopening announcements and big events. And with international travel still heavily restricted and business travel slow to pick up, those destinations have plenty of rooms to fill.

“I was on a call yesterday with an owner of a hotel saying, 'Hey, now that the demand for people staying in beaches, staying in lakes are so high, the [rates] in those environments will be high as well,” said Elliott L. Ferguson, president and CEO of Destination DC. “We might be able to capture indirectly some of that demand.”

Data from TripAdvisor shows that the markets with the slowest recovery for the summer — meaning lots of options for travelers — include New York, Seattle, Los Angeles, Philadelphia and D.C.

Based on booking patterns, Expedia said, destinations including New York, New Orleans, Los Angeles and Orange County, Calif., and D.C. are likely to have more availability than beaches, outdoor recreation hubs and national parks, some of which are “attracting visitors at pre-pandemic levels.”

“It probably doesn’t come as a surprise to see that bigger cities are on our list, as it’s well known that many travelers chose less populated areas over the last year,” Expedia spokeswoman Anna Brown said in an email. “This summer, however, many cities are reopening to welcome back tourists, which means dining, entertainment, live music and shopping are all back on the menu.”

Chicago has announced the reopening of museums, the return of popular tourist site Navy Pier, and the comeback of events such as the Chicago Auto Show and Grant Park Music Festival this summer.

In New York City, which suffered devastating losses from the pandemic last year, the mayor recently set July 1 as the date for a full reopening. Recently, producers announced that Broadway shows would start to reopen in September. The destination, which is predicting more than 36 million visitors this year, is launching a $30 million marketing campaign next month to encourage the recovery of tourism with an early focus on summer visits.

California is targeting June 15 as its reopening date. And while rural areas with fewer people and more space have seen high demand continue since last year, the state’s “gateways” such as Los Angeles, San Diego, San Francisco and Orange County have two-thirds of the hotel rooms.

“That’s exactly where the opportunities are,” said Ryan Becker, a spokesman for Visit California. “My family and I are planning some of those trips ourselves.”

He said the expectation is for tourists to have “very much a typical experience” in the summer, especially since bars, restaurants and cultural institutions are already opening.

“There is a lot to see and do,” he said. “So many of California’s urban destinations have these outdoor experiences built in.”

In D.C., a $2.5 million recovery advertising campaign is targeting travelers among the 50 million people who live within a four-hour drive. International travelers, who spend more and stay longer, are not expected to return for some time still. The city is expecting between 14 and 15 million domestic visitors this year.

“At this point, we’ll take whatever we can get,” Ferguson said. “You’ve got an entire country and global community that’s going after any and all types of visitors out of necessity.”

The destination is promoting its famed museums, monuments and memorials — many of which are free — but also sports, restaurants, rooftops and other part of the city’s culture.

“We know the market is bullish in terms of people wanting to get out and do stuff,” Ferguson said.

Washington, the travel adviser, said that even for destinations that have availability, travelers should not wait too long to lock in their plans once they know what they want to do — after checking cancellation policies. Attractions may still require timed entrances or tickets in advance, and restaurants might have limited amounts of outdoor seating. Hotel prices might go up as more people make reservations.

“If you see something you are interested in — book it! — or you’ll risk losing the price or space,” she said in an email.

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