To the North of Boughton are two parallel tunnels some 3 metres underground. Both are constructed of dressed stone and have arched roofs. They are approximately 2.5 metres across by 2 metres high.

There has been conjecture regarding their original purpose ranging from walkways to allow the gardeners to go about their business without being seen from the House to ice houses.

However recent studies suggest that they may have been used to provide a head of water for the fountain in the Grand Etang, which could, like those at Versailles, be played when important guests arrived at the House.

The tunnels are not generally accessible for Health and Safety reasons.