The Bois Sacré — "Sacred Wood" — is an ancient grove of olive trees a short walk south of the centre, gathered around the shrine of Sidi Yacoub al-Kabir, a 16th-century Sufi saint traditionally considered the founder of Blida. The olives are said to have been planted by the saint himself, and some of the gnarled trees are clearly several centuries old.
The grove is open and free to walk through; the shrine itself is a small whitewashed building with a green-tiled dome, still in use as a place of prayer and pilgrimage. Local women come on Thursday afternoons to leave small offerings and ask for blessings. Combine with a walk along the rose gardens of the Mitidja plain just beyond.