Erddig Motte

A section of Wat's Dyke approximately 1,500 metres (4,900 ft) long runs north to south through the park, to the west of the house. It consists of a bank up to 2 metres (6.6 ft) high and a ditch to its west, and was probably built in the eighth century by Æthelbald of Mercia to mark the boundary between his kingdom and the Kingdom of Powys. Part of Wat's Dyke is incorporated into a Norman motte-and-bailey castle, called "Wristleham" in a pipe roll dated to 1161, which is located within the park on a bluff above the confluence of the Black Brook and River Clywedog.

The estate buildings include the joiners' shop and smithy, the Midden Yard (with its saw mill and cart sheds), and the Stable Yard (with its stables and tack room, carriages and vintage bicycles and vintage cars). In the house are the laundry, bakehouse, kitchen and scullery. The nearby river supplied a source of water, which was pumped uphill by a hydraulic ram, the water entering the ram via a feature known as Erddig's Cup and Saucer.

In 2003, Erddig was voted by readers of the Radio Times and viewers of the Channel 5 television series Britain's Finest Stately Homes as "Britain's second finest". In September 2007 it was voted the UK's "favourite Historic House" and the "8th most popular historic site" in the UK by Britain's Best. Erddig was awarded National Heritage Museum of the Year in 1978, a joint award with the Museum of London.