In celebration of the summer opening of the water park, Rainbow Pool, in Kokuei Showa Memorial Park the first 15,000 people to show up for that day get free admission.
First come, first serve, so find your way down to the park early or be prepared for a line.
Admission: normally 2,300 yen, but if you are the first 15,000, it is FREE.
HOWEVER, you need to pay the park entrance fee of 410 yen to enter the park.
2 minutes from Nishi Tachikawa Station