At Léran, go to the Place des Tilleuls. Beyond there, follow the yellow markers towards the castle which you’ll pass as you stroll down the long avenue of plane trees which will lead you to the cattle farm known as "La Nouvelle".
If this walk seems too long for you, there are two variations :
1 - Léran - St Quentin - Belloc - Léran : 7 h /21 km
2 - Camon - Belloc - St Quentin - Lagarde - Camon : 5 h 30 /16 km