The Old Croton Reservoir in front of Belvedere Castle that Christopher Sees (or Doesn’t)
The pond in front of Belvedere Castle was once part of a much larger body of water called the Croton Reservoir.
If you look in the upper left hand corner of the photo, you will see several baseball diamonds which is as far as the original reservoir extended. Even this wasn’t enough to quench the thirst of the growing city, so it was filled in and a new reservoir built further north, leaving what is now known as Turtle Pond as the only reminder of its prior existence.
If you’ve read the first few pages of Central Park Story Book One, you’d know that Christopher ‘sees’ the old Croton Reservoir which makes him question his sanity.