This is Tokyo's largest public facility for children -- and it's absolutely free. There are toddler areas, indoor gyms, computers, a crafts corner, musical instruments, and a rooftop playground (open weekends and holidays), as well as a minitheater with frequent showings of free films and monthly events and programs (in Japanese only). Although the hall is not as extensive or sophisticated as the National Children's Castle, the price is right and it's good for a rainy day. Note: Sadly, this facility is slated to close in March 2012 (though a skate park is slated to open nearby).