The Grade I-listed monument offers spectacular views out over the countryside and it will be open as a fund-raising event run by Alnwick Lions.
Built in the 18th century by the 1st Duke of Northumberland in memory of his wife, Elizabeth Percy, 1st Duchess, the 26-metre-tall folly was designed by the famous Scottish architect, Robert Adam.
The event takes place on Sunday, August 21, from 11am to 4pm. Entry is free, with the Lions asking for donations to support the work the group does in the local community.
A shuttle bus will run to and from the parking area and refreshments will be provided. Dogs are not allowed access to the park.