Tsuyu is Japan’s rainy season. How bad can it be, you ask? While far less torrential than your average Indian monsoon, tsuyu tends to soak June, and submerge part of July. It doesn’t rain incessantly, but interim days steam like a Turkish bath and fill with squadrons of mosquitoes. To be fair, venturing outside during the rainy season is not all misery and blood dona­tion. Temples are often misty and deserted and there are gorgeous sights to reward the outdoors adventurer — hydrangea blossoms in Kamakura come to mind. Below, you’ll find indoor educational and entertaining destinations that are, in honor of the season, all wet.

You’ll immediately get the drift of the Museum of Mar­itime Science (Fune no Kagakukan); it’s shaped like a cruise ship. Located near Odaiba, this lesser-known-museum is a titanic delight which caters to all ages. For the very young, simply being at the helm of the submarine will float the day; for older salts, the histori­cal displays, engines and props will enthrall. Proximity to the other attractions of Odaiba and a multitude of kid-friendly restaurants is an added plus. Open 10am-5pm (6pm on weekends, holidays, and summer season); Tel. 03-5500-1111; Fune no Kagakukan Station (Yurikamome Line).

Wow your junior Cousteau with one of the city’s awesome fish tanks. At any of the following aquariums (suizokukan in Japanese), be prepared to spend a lot of time and a similar amount of yen.

The catch of the day is the Epson Aquastadium, newly opened April 2005, in the popular Shinagawa Prince Hotel complex, which also features IMAX movies, bowling, karaoke, and tennis. Little ones might feel ail-too Nemo-like threading the underwater shark and ray tunnel, but will love the dolphin and sea lion acts. Rides, theater, and tank-side dining are optional extras inside the stadium. Noon-10pm Mon.- Fri.; Sat. 10am-10pm; Sun. and Nat. Holidays 10am-9pm; Tel. 03-3440-1111; Shinagawa Station.

In the immediate vicinity is the Shinagawa Aquarium (Open 10am-5pm; Closed Tuesdays; Tel. 03-3762-3431). Also boasting a sea-through tunnel and a whole kettle of fish, this one includes a popular critter petting pool. You can round out the marine theme by catch­ing a water bus shuttle between Shinagawa Aquarium, the Museum of Maritime Science and Hinode Pier.

Believe it or not, there are several other aquariums in town, but the Sunshine International Aquarium deserves lofty accolades for its astonishing location on the tenth floor of the World Import Mart Building, in Sunshine City. 37,000 fish, Rockhopper penguins, and elegant jellyfish cavort far above sea level in a facility that offers cool parent-child “sleeping with the fishes” overnight adventures (call for lottery and price details). Open daily 10am-6pm (6:30pm on weekends and holidays); Tel. 03-3989-3466: Ikebukuro Station.

It’s a bit of a “Westward Ho!” train ride, but Toshimaen Hydropolis is the ultimate wet-your-suit experi­ence. There’s a massive wave pool, tons of slides, and seven other pools to choose from, and the amusement park itself is always there if the skies clear. Many of Toshimaen’s rides are built for older kids (the Log Ride and the gargantuan Pirate Ship ride are superior examples, plus they fit our theme). For the timid, attractions include a hand-carved wooden carousel an aging beauty alone worth the trip. Toys “R” Us looms nearby, an excellent opportunity to stock up on birthday supplies and holiday gifts. The amusement park is open 10am-6pm daily except Tues. and Wed., until Jun. 25, when pools open and park hours are daily and extended. Tel. 03-3990-8800; Toshimaen Station, Oedo Subway.

Pour it on for your budding Einstein at the Science Museum Tokyo, the city’s best hands-on funhouse for interaction with motors, magnets, and visual percep­tion games. Displays featuring “Magical H2O,” and a “Tornedo in a Bottle” are included, natch! Built in 1964, but with constantly updated displays, the seven floors (five above and two below) beg kids to get their feet wet in a relationship with science. Open 9:30am-4:50pm; Tel. 03-3212-2440; Takebashi Station, Tozai Line. Cool English website features a new scientific fact or historical event each day: www.jsf.or.jp/eng/

Last, you won’t get soaked at the Ariake Water Mu­seum; entrance is free. Built over the Ariake water supply station in Odaiba, the museum has three floors of exhibits all devoted to the wonders of water, and you can take a (slightly kitchy) tour of the pumps below. The virtual reality theater features a white-water rafting ride, the real rush is the interactive displays on water. You’ll slake your thirst for knowledge but don’t look for bottled water here; vending machine are filled with other beverages! Open 9:30am-5:00pm (closed Mondays) Tel. 03-3528-2366; Ariake Station, Yurikamome Line.