Duncombe Park is a Baroque mansion that was completed in 1713. The property is currently owned by Lord and Lady Feversham. It is built on a plateau overlooking Helmsley, Helmsley Castle and the valley of the River Rye. It is set in hundreds of acres of land and part of the house and large gardens are open to the public. You can easily spend upwards of a day looking around the house and exploring the gardens.
We last went for a walk around Duncombe Park in June 2010 and it was absolutely sweltering hot. The high-rised position of the property didn't help. Fortunately there are lots of trees that gave some welcome shade from the sun. Anyhow exploring the gardens will reveal several follies along with some excellent views.
Duncombe Park hosts a fair few events such as wedding fairs, craft fairs and plant fairs. It may be worth checking their events page before making a visit to see what's on. That way you may be able to make a whole day of your visit.
Discover Yorkshire Gallery - Duncombe Park
Duncombe Park Official Website
Wikipedia - Duncombe Park