Best natural monuments around Sint-Pieters-Leeuw are found in this municipality in Flemish Brabant, Belgium. The region is characterized by its transition from the rural Pajottenland to the urbanized Zenne valley. The primary natural monument is the Zuunvallei, a nature reserve encompassing diverse landscapes such as wet meadows, marshland, and a meandering stream. This area offers opportunities to experience rich biodiversity and varied natural features.
Last updated: June 28, 2026
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I recommend this route without hesitation, it is a beautiful forest, I just visited it a few weeks ago and was amazed; in full growth stage of the hyacinths or bluebells. A must-see destination in Brussels.
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This tour goes for kilometers through the forest. In spring it is beautiful with the hyacinths and wood anemones. In summer nice and cool.
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A sunken road is a road that is so deeply worn that it lies between two slopes. It is the result of centuries of use and erosion. The most beautiful sunken roads can be found especially in hilly areas with a subsoil that easily forms steep walls, such as in Haspengouw and Hageland.
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Enjoying the Sonian Forest is easy from the various access gates. These access gates are located on the edge of the forest, are easily accessible and are therefore the ideal starting point to explore the forest. There are eight access gates. Information about this can be found at https://www.zonienwoud.be/praktisch/toegangspoorten/
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The Sonian Forest, also known as the Zoniënwoud, is a large forest area centrally located in Belgium, southeast of Brussels. It covers approximately 4,421 hectares and is best known for its old beech trees, some of which are over 200 years old. The forest has a rich history dating back to the Iron Age and has had various functions over the centuries, such as providing firewood and timber for the construction of houses and ships, and as a backdrop for hunting scenes. The current forest landscape with deciduous trees has its origins in the Austrian period (1714-1795).
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Always beautiful, spacious and varied forest
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The Sonian Forest is an exceptional, vulnerable and ancient forest that is also recognized as a UNESCO World Heritage Site. The forest extends across the three Belgian regions and is one of the best-known and most visited green spaces in the region.
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Very quiet and beautiful for driving and walking.
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The region offers diverse natural features. The primary natural monument is the Zuunvallei, characterized by the meandering Zuunbeek stream, wet meadows, and marshland. You can also find unique geological formations like the Hollow Way in Neigembos, which features sunken roads formed by centuries of erosion. Additionally, the nearby Hallerbos — The Bluebell Forest is famous for its stunning carpet of wild hyacinths in spring.
The Zuunvallei is a haven for wildlife, especially birds. You might spot migratory birds like the Snipe, Common Sandpiper, and Green Sandpiper, particularly in the Volsembroek area. It's also known for a large population of Green Frogs. The Oude Zuun section is home to over 22 species of butterflies, including the Brown Hairstreak and Orange-tip. The broader Sonian Forest also hosts a variety of animals.
Yes, the Zuunvallei provides excellent opportunities for hiking and walking, with trails leading through picturesque and varied landscapes. For more options, you can explore various hiking routes around Sint-Pieters-Leeuw, including easy paths like 'Fields and the Zuunbeek – Saint Peter's Church loop'.
The best time depends on what you wish to experience. Mid-April is ideal for witnessing the enchanting bluebell bloom at Hallerbos — The Bluebell Forest. Spring is also when the Green Frogs create a 'spectacular concert' in the Zuunvallei. Summer allows you to see Galloway cattle grazing in Volsembroek. The diverse landscapes offer beauty throughout the year, with autumn providing vibrant colors.
Many natural monuments are family-friendly. The Hallerbos — The Bluebell Forest and the Sonian Forest are popular choices for families. The Drowned Children Ponds also offer a pleasant setting for a family outing with picnic benches. The Zuunvallei has walking paths that allow visitors to encounter grazing Galloway cattle, which can be an engaging experience for children.
The Sonian Forest is generally dog-friendly, offering ample space for walks. It's always recommended to check local regulations or signage at specific natural monuments for any restrictions regarding dogs, especially in nature reserves like the Zuunvallei, to protect wildlife.
Yes, the Hollow Way in Neigembos is a notable historical site, featuring veteran trees that survived the First World War. The sunken roads themselves are a result of centuries of human and cart traffic. The Sonian Forest also has a rich history dating back to the Iron Age, with its current landscape shaped over centuries.
Beyond hiking, you can find various outdoor activities. There are several running trails, including the 'Loopomloop Sint Pieters Leeuw'. For mountain biking enthusiasts, there are MTB trails such as the 'Zuun Great Pond – Singletrack along the Zuunbeek loop'.
The Zuunvallei offers surprising open and diverse nature with views of the Brussels skyline, transitioning from the rural Pajottenland to the urbanized Zenne valley. The Drowned Children Ponds also serve as a scenic viewpoint within the Sonian Forest.
The Zuunvallei has informational panels at its entrances, and some walking paths are accessible, allowing visitors to get close to the grazing Galloways. While some paths in the Zuunvallei are unpaved, offering an authentic natural experience, specific accessibility for wheelchairs may vary. It's best to check individual trail conditions if you have specific accessibility needs.
Yes, Natuurpunt Leeuwse Natuurvrienden, which manages the Zuunvallei, regularly organizes guided walks and management workdays. These can be a great way to learn more about the area's biodiversity and conservation efforts.
Among the most popular natural monuments are the Hollow Way in Neigembos, known for its unique geological formations and veteran trees. Another highly cherished spot is Hallerbos — The Bluebell Forest, famous for its stunning spring bloom. The vast Sonian Forest, a UNESCO World Heritage Site with ancient beech trees, is also a favorite.


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