Tree tunnel of Haut-Maret, Protected heritage tree tunnel in Theux, Belgium.

The tree tunnel of Haut-Maret is a hornbeam bower 573 m long in a straight line, formed by 4,700 plants set in a double row and trained to arch inward into a cradle. The slender dark trunks line both sides of a bare-earth path strewn with fallen leaves, and their joined branches close overhead into a green canopy that ends at a small opening of light.

The hornbeam tunnel was planted in 1885 by industrialist Michel Nys, who named it after the nearby Château des Hauts-Marais. He employed road workers Victor Charlemagne Thorez and Mathieu Compère, while village blacksmith Adolphe Cortin made the metal frame. During the Eighteen Days' Campaign, German tanks damaged nearly half its length; that section was not restored and in 1995 was named Drève Thorez. The surviving part was classified in 1979 and restored in 1985.

The tunnel is maintained by students from the agricultural school in La Reid, who work on this green corridor as part of their practical training. This ongoing care has turned the place into a living learning environment where nature and education meet.

The tunnel lies between Chemin de Quarreux and Rue Hautregard in La Reid, a section of Theux. It is open only to walkers and cyclists, from sunrise to sunset. The surviving stretch runs 573 m in a straight line, with a small opening of light visible at the far end.

The hornbeam tunnel is named after the nearby Château des Hauts-Marais. When industrialist Michel Nys settled there, he had the double row planted in 1885 by road workers Victor Charlemagne Thorez and Mathieu Compère, with the metal frame made by village blacksmith Adolphe Cortin.