Order lunch by the pool, exercise with celebrity instructors, party on world-class beaches with music and great food.

Summer in the Hamptons and Montauk does not come cheap and even if you wanted to, finding a hotel to stay overnight can be tricky, since many are booked through summer.

But some open their doors -- and patios -- for day trippers, offering use of amenities usually reserved for overnight guests, including the pool, exercise classes and beachside barbecues.

All give a taste of the high life on the East End at a fraction of the peak summer charges.

"The beaches are magnificent, the estate houses are beautiful . . . and the shops are exquisite," says Dede Gotthelf, owner of the Southampton Inn, which offers day passes.

PLAY FOR THE DAY

Tennis, anyone? How about a dip in the pool?

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Southampton Inn offers a day pass to its idyllic hotel, where rooms often go for $300 a night or more.

The pass includes an hour of tennis (rackets can be rented), a swim in the pool and the crown jewel of residency perks: a free ride in the hotel's polka-dot shuttle bus to Cooper's Beach, where parking passes for nonresidents cost $40 a day.

The hotel's day pass also entitles guests to use the showers, (complete with towels, soaps and shampoo), gives kids time in the game room and comes with a $20 voucher to the hotel's dining room, OSO.

Gotthelf says it's a great opportunity for those living west of the Hamptons to spend a day at an East End hotel. "In the Hamptons, as we all know, it can be busy in the summertime, and it can be costly," she says.

Only 10 passes are offered per day, and weekends are almost sold out, so it's best to reserve ahead.

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WHEN | WHERE Daily at 91 Hill St., Southampton. Must register in advance.

INFO 631-283-6500, southamptoninn.com

COST $100 per person

BEAUTY AND EXERCISE

Health and beauty are big business in the Hamptons. At the Montauk Surf Lodge, daytrippers can spend several hours at two "Surfside Salutations" -- special events that fuse exercise with summer fun.

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July's session starts with a yoga session with Heather Lilleston. August's event features a dance cardio workout with Anna Kaiser, whose clients include Shakira and Kelly Ripa..

After each, activities range from beauty-related workshops such as making your own after-sun oil and blending teas, to a braid bar (the newest thing for longer hair, and great for the beach), even paddleboarding ($20 extra).

Enjoy the hotel's beach or -- for an extra $40 -- stick around for a specially designed healthy brunch.

"We just wanted to create our perfect summer day," says Alexia Brue, publisher and co-founder of Well+Good, a media company focusing on health, fitness and beauty that is co-hosting the events.

WHEN | WHERE 9 a.m.-2:30 p.m. July 11 (yoga) and Aug. 22 (dance cardio) at 183 Edgemere St., Montauk. Must register online.

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INFO 631-483-5037, wellandgood.com

COST $40 ($40 extra for brunch)

BBQ AT THE BEACH

One of the more upscale resorts on the East End, Gurney's has opened its beach club, located right on the sand, on Saturdays to those who are not staying at the hotel with an afternoon BBQ.

The sun and beach scene gets started at 11 a.m. with grilled fare of 18-hour-slow-cooked short ribs and jerk chicken, as well as hot dogs and assorted sides. Drinks are extra at the beachside bar and patrons are welcome to hit the surf. The DJ gets the crowd up and dancing in the sand from 1 p.m. until about 6 p.m.

Good to know: The resort's traditional yellow-and-white beach cabanas can be reserved by non-guests. Groups of up to eight people can set up for the day, just know there's a $500 food and drink minimum on weekdays, $1,500 on weekends.

GURNEY'S MONTAUK RESORT AND SEAWATER SPA

WHEN | WHERE 290 Old Montauk Hwy., Montauk. Reservations required.

INFO 631-668-2345, ext. 3200 or email BeachClub@gurneysmontauk.com

COST $14-$29 (extra $19 for lobster).