Go west. If you're looking for amusement parks in the Tokyo area, the surviving ones seem to all be west of the city center. Some may be northwest like Toshimaen, others southwest like Yokohama CosmoWorld, but the east side just doesn't have much to offer. Sure, straight north is Tobu Zoo and Asakusa's Hanayashiki Park is on the eastern side of the city, but they have other attractions that draw the crowds (animals and history, respectively). That might be due to the existence of a certain mouse on the eastern side of Tokyo, though I'm sure weather and traffic patterns (including train lines) make a difference.
Head west a little bit on a train and grab a bus, and you can go to Tokyo Summerland. The blue and red letters above the second floor of the entrance building announce that you've arrived. The building holds the massive indoor water park too.That park is called Adventure Dome, and as you see it has a large wave pool and some slides in the distance. Outside are a few more slides as well, though they are closed at this time of year. The indoor park is heated, and I'm sure the water is too. I visited last November on a chilly afternoon and it was quite warm and humid inside.
A few small dry attractions are housed here as well, including this little safari train. The area next to the entrance has a lot of merchandise space, including swimwear and supplies for the water park, as well as some food choices.
Heading out back you come across a selection of rides. Here's a freefall and a flat ride.
There's a small carousel.
This is one of those fast spinny rides that are just painful for me.
Do you want to play a game? There are a few carnival-like games somewhere around here, I'm sure.
The swinging pirate ship was fairly popular. There are some mazes and other attractions in the park, too.
But I'm here for the coaster.
Hm. It looked better from farther away. Is this a bad sign? The theme park area was pretty empty, though as soon as I got in line a bunch of other people joined me and we ended up with pretty close to a full train.
It's an old looping coaster and it isn't very big. It looked pretty old, too, to go with the rest of the park. I'm not sure how much they've put into the rides in the past few years. It's a big difference compared to the water park.
It was getting dark out, but you can still see how grimy (moldy?) the tracks look.
There's a little corkscrew loop after the loop too, by the way. I'm not exactly sure what the house is for in the middle of the park right next to the coaster. Does someone live there?
Here's a better view of the layout from the Ferris wheel.
Another brave group of riders head up the hill..
And through the loop they go! It wasn't a horrible coaster, but despite having an all-you-can-ride ticket I didn't go for a second spin. I ended up trying several of the other attractions, and went on the drop ride three or four times - yes, the painfully rough drop ride was better than the coaster.
Here's a view of most of the park - it sits on the east side of a mountain so the sun sets sooner here than the neighboring valley - not the ideal place for a theme park with water rides.
Here's a zoomed view of the indoor water park building and the drop ride.
And another view of the free fall ride... normal exposure...
...and here is a longer exposure.
The water park was pretty crowded on a Sunday late afternoon but as I mentioned the rides part of the park wasn't. I could walk on to all the rides. Summerland felt almost abandoned, similar to many of the theme parks around the country. Several were built when times were good and money flowed like water from a hot spring, but financial issues have closed several parks and left most of the rest barely hanging on. Disney and Universal Studios certainly haven't helped things either. I really can't think of any truly new coasters in Japan outside of Disney, Universal, and Fuji Q.
A quick check of the Roller Coaster Database shows that no new coasters opened in Japan this year; two kids coasters and a replacement coaster (which is pretty good) for Joypolis opened last year, and only one new coaster is mentioned for next year, though it could be really fun.
Water Adventure Tokyo Summerland (even the water park comes first in the name now) is open from March through November with varied hours, and is closed one or two days a week in the spring and fall. Admission for adults starts at 2000 yen, with a free pass for the rides adding an additional 1000 yen; prices are higher in the summer when the outdoor water attractions are open. It's a 40 minute train ride from Shinjuku Station to Hajima Station, then another 10 minutes to Akigawa Station. Finally, a 10 minute bus will take you right to the park's front door.