The Castle continued to serve no significant function until 1919 when the United States Weather Bureau started using the Castle to record weather data for Central Park since the Castle sat elevated above the Park. The weather for Central Park was recorded on Fifth Avenue and 64th Street prior to the move. To better prepare the Castle for weather observation functions, doors and windows were added and offices were built inside the Castle. The Weather Bureau still uses the Castle to record weather data today, though most of it is automated and the offices have been moved elsewhere since the 1960s.
After the Weather Bureau left, the Castle was neglected for a time, and it fell into disrepair by the 1980s. However, in 1983, the Central Park Conservancy stepped in to renovate the Castle and turned it into a visitor's center with a new turret and rebuilt pavilions. An observatory, known as the Henry Luce Nature Observatory, was added in 1996. The Observatory includes nature exhibits and bird-watching tools.