The best indoor water parks all have one great thing in common: they're weather-proof. Even if it's raining or snowing outside, they consistently hover around a balmy 84 degrees. But there's a lot more to love about these aquatic playgrounds, because they're often attached to resorts with themed guest rooms and other family-friendly activities. Whatever your reason for going, here are eight indoor water parks you can splash into all year long.

Great Wolf Lodge | Grapevine, TX

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Claim to fame: It's part of the largest family of indoor water parks in the United States (there are 12 others).

What's inside: A four-story treehouse with a 1,000-gallon tipping bucket, six water slides, two jumbo hot tubs, safe play zones for kids, a wave pool, and a lazy river.

Most extreme water slide: The Howlin' Tornado, a six-story funnel that swirls riders 30 feet up the sides in a four-person raft.

Does it offer day passes?: You must be a hotel guest to gain entrance to the park.

Hotel perks: A spa and kids' spa, numerous dining options, and themed guest rooms with bunkbeds.

Kalahari Resort | Sandusky, OH

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Claim to fame: It was named one of America's coolest indoor water parks by Conde Nast Traveler.

What's inside: A 50,000-gallon Flowrider, 10 water slides, indoor and outdoor hot tubs, safe play zones for young kids, a wave pool, and a lazy river.

Most extreme water slide: The Zip Coaster, a roller coaster-water slide hybrid that propels riders through free falls and turns at speeds of up to 20 miles per hour.

Does it offer day passes?: Yes

Hotel perks: A safari-themed animal park, mini bowling and mini golf, an arcade, numerous dining options, and suites that comfortably sleep up to 36.

Fallsview Indoor Waterpark | Niagara Falls, Ontario

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Claim to fame: This is said to be North America's largest indoor water park, and it was named one of the 10 best indoor water parks in Canada by TripAdvisor.

What's inside: 16 waterslides, Hot Springs Horseshoe whirlpool, a wave pool, an outdoor sundeck with a pool, a splash park, and a tipping bucket.

Most extreme water slide: Ride by yourself or with your friend down the Toob Tower, where you can choose from four different routes.

Does it offer day passes?: Yes.

Hotel perks: Guests of the Skyline Hotel & Waterpark have access to the Fallsview Indoor Waterpark. Shop for deals at the Skyline Hotel here.

H2Oooohh Indoor Water Park | Lake Harmony, PA

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Claim to fame: H2Oooohh features the state's first indoor Flow Rider boardsport facility, so you can practice surfing in the Poconos.

What's inside: Three water slides, a wave pool, Jungle Play area, the Oasis snack shack, and the Leapin' Lillypads crossing area.

Most extreme water slide: This water park features three different water slides, each 4-stories tall.

Does it offer day passes?: Yes

Hotel perks: The water park is connected to Split Rock Resort. Look into the resort's "Splash and Stay" package for discounted admission to H2Oooohh.

KeyLime Cove Indoor Waterpark Resort | Gurnee, IL

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Claim to fame: It's the largest indoor water park in the United States.

What's inside: Five water slides, an adults-only hot tub, safe play zones for young kids, a gentle wave pool, and a lazy river.

Most extreme water slide: The Hurricane Vortex, a whirlpool slide that ends with a plunge into the lazy river.

Does it offer day passes?: You must be a hotel guest to gain entrance to the park.

Hotel perks: An 8,000-square-foot arcade, an arts and crafts room with daily activities, numerous dining options, and tropical-themed rooms and suites.

Maui Sands Resort & Indoor Waterpark| Sandusky, OH

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Claim to fame: The Maui Wowie Bowl Slide, where you'll brave the conditions inside a massive bowl before a final drop into the water below.

What's inside: Two half-pipe body slides, two tube slides, a treehouse play area, water basketball hoops, lazy river, kiddie pool, and a vortex pool.

Most extreme water slide: The Hammerhead Plunge, a winding, twisty slide that reaches speeds of up to 45 mph.

Does it offer day passes?: Yes

Hotel perks: Many rooms at Maui Sands come with water-park passes. Inquire with the hotel to ensure a special rate.

Water Park of America | Bloomington, MN

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Claim to fame: It's the tallest indoor water park in the United States.

What's inside: A Flowrider that moves at up to 30 miles per hour, a multi-story fort with a 500-gallon tipping bucket, four water slides, a hot tub, a wave pool, and a lazy river.

Most extreme water slide: The Eagle's Nest, a five-story body slide that begins on the 10th floor and ends in a giant pool.

Does it offer day passes?: Yes

Where to stay: There's no hotel attached to the indoor water park, but you can stay right across the street at Radisson Hotel Bloomington by Mall of America. Search coupons for Radisson here.

Splash Lagoon | Erie, PA

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Claim to fame: It's home to the largest wave pool in the eastern United States.

What's inside: A five-story tiki treehouse with a treetops ropes course and giant tipping bucket, eight water slides, three hot tubs, a safe play zone for young kids, a wave pool, and a lazy river.

Most extreme water slide: The Hurricane Hole, a whirlpool slide that reaches speeds of up to 40 miles per hour.

Does it offer day passes?: Yes

Where to stay: There are three hotels attached to Erie PA water park: a Holiday Inn Express & Suites, a Residence Inn by Marriott, and a Comfort Inn & Suites. Find other nearby hotels in Erie here.

Boyne Mountain Water Park | Boyne Falls, MI

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Claim to fame: It's Michigan's largest indoor water park.

What's inside: Five water slides, two hot tubs, safe play zones for young kids, an indoor surfing wave, a wet climbing wall, and a lazy river. Oh, and a "water avalanche" that dumps 800 gallons every 15 minutes.

Most extreme water slide: The Vertigo Slide, a tube slide that shoots riders into a giant whirlpool.

Does it offer day passes?: Yes

Hotel perks: A ski hill, ziplines, horseback rides, a 36-hole golf course, and chalet-like guest rooms.

Photo: Courtesy of Avalanche Bay Indoor Water Park

What's the best indoor waterpark you've ever been to?