Osny circular to Boissy-l'Aillerie

The hike begins in front of Osny Town Hall in the beautiful setting of Château Grouchy and its park bordered by a pond. The walk heads north-west to the town of Boissy-l'Aillerie, returning south and then east to the starting point via Grouchy Park.
Much of the route is away from roads with motor traffic.

Details

26879547
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  • Walking
    Activity: Walking
  • ↔
    Distance: 9.23 km
  • ◔
    Average duration: 2h 50 
  • ▲
    Difficulty: Easy

  • ⚐
    Back to start: Yes
  • ↗
    Ascent: + 57 m
  • ↘
    Descent: - 56 m

  • ▲
    Highest point: 86 m
  • ▼
    Lowest point: 33 m
  • ⚐ Country: France
  • ⚐
    Area: Vexin
  • ⚐ City: Osny (95520)
  • ⚑
    Start/End: N 49.066155° / E 2.060929°
  • ❏
    IGN map(s): Ref. 2313OT
  • Hour-by-hour weather

Description of the walk

The starting point is in front of the Château de Grouchy.

(S/E) First, facing the château, take the path on the left until you reach the wash house to join the northern exit of the park. Continue along the Font path which climbs up to the village of Immarmont, then continue along Rue Paul Doumer on the left. You will reach a four-way crossroads.

(1) Turn right at a 90° angle to climb to the top of the village. You will reach the crossroads of Chemin de la Croisette and Boulevard de la Libération.

(2) Turn left and follow the road alongside the fields. Cross the D22 roundabout with caution, then continue straight ahead. After the Pôle Médical, turn left onto Chemin de Gérocourt.

(3) Continue along this path and turn right onto Chemin de la Justice for 230 metres, then continue straight ahead on a dirt track. After 200 metres, you will find a path on the left that descends into a wood.

(4) Take this path and, when you come out of the woods, turn slightly left onto Rue Veuve Quatremain in the village of Boissy l'Aillerie.

(5) After 170 metres, turn left onto Rue Macaigne-Fortier, then after 100 metres, turn right down Rue de La République until you reach the level crossing.

(6) Cross the level crossing, then turn slightly left to continue on the D22 via Allée du Moulin. After the 90° bend, continue along Rue Pasteur, then along Route d'Ableiges for 1.25 km until you reach the village of Le Réal. On the left, take Rue de Panama, following the sign for "Marais du Missipipi", then immediately turn right and cross the level crossing on the left.

(7) Continue along the path on the left, which then turns right. At the next crossroads, turn right onto Chemin des Côtes de Bizières to return to the crossroads at the start of the route.

(1) Go down Rue Henri Lechaugette on the right to the western entrance of Grouchy Park.

(8) Enter the park, turn right, walk along the edge, then at the small car park, turn left into the large avenue until you reach the pond. Go around it on the right to return to the Château de Grouchy car park (S/E).

Waypoints

  1. S/E : km 0 - alt. 41 m - Château de Grouchy car park - Gare d'Osny
  2. 1 : km 0.75 - alt. 53 m - Crossroads of the circular loop
  3. 2 : km 1 - alt. 71 m - Immarmont North
  4. 3 : km 3.08 - alt. 85 m - ZA Nord Boissy l'Aillerie
  5. 4 : km 3.84 - alt. 71 m - Chemin de la Justice
  6. 5 : km 4.31 - alt. 46 m - Vaugoulé
  7. 6 : km 4.86 - alt. 42 m - Boissy level crossing
  8. 7 : km 6.38 - alt. 39 m - Le Réal level crossing
  9. 8 : km 7.95 - alt. 37 m - Western entrance to the park
  10. S/E : km 9.22 - alt. 41 m - Return to Château de Grouchy

Notes

On a small section of the route, it is necessary to walk in single file.
No special equipment is required, but walking poles will provide comfort on some steep trails.

Worth a visit

(S/E) At the Château de Grouchy, you can visit the William Thornley Museum and the Firefighters Museum in an annex.
Between (2) and (3) Boulevard de la Libération is in fact a path that was partially concreted during theSecond World War and is now closed to traffic.

Reviews and comments

4.2 / 5
Based on 8 reviews

Reliability of the description
4.3 / 5
Ease of following the route
4.3 / 5
Route interest
4 / 5
User 27838713

Overall rating : 5 / 5

Date of your route : Oct 13, 2025
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★★ Very good
Very busy route : Yes

Pleasant route
Not complicated
Easy to repeat

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afoe
afoe

Overall rating : 4.7 / 5

Date of your route : Oct 13, 2025
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★☆ Good
Very busy route : No

varied, rural route with sections through woods. Beautiful views of Montgeroult Castle.
easy hike on well-drained terrain.

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GCl
GCl

Overall rating : 4 / 5

Date of your route : May 19, 2025
Reliability of the description : ★★★★☆ Good
Ease of following the route : ★★★★☆ Good
Route interest : ★★★★☆ Good
Very busy route : No

Overall, the route is pleasant.
The description makes it easy to follow the hike without too much difficulty.
Street names are often indicated, but the street name signs are often only placed on one side of the street, so you have to walk down the street in question to confirm that you are on the right route.
However, apart from the wash house, where the description is vague and the name of the street to take is truncated (Sentier de la Font instead of Fontaine), we did not encounter any real difficulties.

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SylvieDelap
SylvieDelap

Overall rating : 4.7 / 5

Date of your route : Mar 04, 2024
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★☆ Good
Very busy route : Yes

The highlight of the route is the castle and its grounds.

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Yohann_1981
Yohann_1981

Overall rating : 4 / 5

Date of your route : Jul 17, 2023
Reliability of the description : ★★★★☆ Good
Ease of following the route : ★★★★☆ Good
Route interest : ★★★★☆ Good
Very busy route : Yes

Pleasant hike.
Very easy.
Beautiful views in some places.

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Martine Jclaude
Martine Jclaude

Hello,
Thank you for your helpful comments.
I have made the changes you requested for the hike, and I believe it has now been published.
Martine J Claude

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Melauric70
Melauric70

Overall rating : 3.7 / 5

Date of your route : Mar 27, 2023
Reliability of the description : ★★★★☆ Good
Ease of following the route : ★★★★☆ Good
Route interest : ★★★☆☆ Average
Very busy route : No

2 wash houses along the route.
A short, easy walk with no difficulty.

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joelle C&R
joelle C&R

Overall rating : 4 / 5

Date of your route : Feb 26, 2023
Reliability of the description : ★★★★☆ Good
Ease of following the route : ★★★★☆ Good
Route interest : ★★★★☆ Good
Very busy route : No

Easy hike in cold but sunny weather with a light breeze. Spring is coming.
The only part of the route that could be avoided: at point 2, instead of walking along a boring industrial area, it is better to turn left at the roundabout onto the D22 and go straight to Chemin de la Justice.

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paulette.legendre
paulette.legendre

Overall rating : 3.3 / 5

Date of your route : Oct 14, 2022
Reliability of the description : ★★★☆☆ Average
Ease of following the route : ★★★☆☆ Average
Route interest : ★★★★☆ Good
Very busy route : No

This easy route requires additional details if you are walking without using GPS. In particular, when you reach the industrial estate, specify that you should continue straight ahead, keeping the industrial estate on your right. Also, in Boissy l'Aillerie, specify that you should cross the railway line and do not indicate the number of the departmental road, or else indicate the correct number... Other fixed landmarks could be indicated, such as the water treatment plant, buildings, calvaries, etc. Finally, distances, even approximate ones, could be indicated.
Otherwise, we really appreciate Visorando
. Paulette

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