New playground scheduled for construction at Billings Castlerock Park in 2021 Castlerock Park in Billings getting new playground and last updated 2021-01-06 00:16:41-05 BILLINGS â Castlerock Park in Billings will have a new playground constructed on the west side of the park in 2021, according to a master plan that was shown to the Billings City Council Monday night. The playground is one of many improvements identified in the Castlerock Park master plan that has a total build cost estimated at $11.9 million. Across the 25-acre park in Billings Heights, new amenities proposed include an event pavilion, amphitheater, basketball court, community center, pickleball courts, picnic seating, restrooms and others.