Fontainebleau is worth visiting year-round, but the season makes a real difference to what you get out of it.
Autumn (October–November) is the best time. The forest turns spectacular shades of red and gold, the palace is less crowded than in summer, and the bouldering conditions are ideal — cool temperatures and dry rock make for the best friction on the sandstone. Weekend crowds in the forest can still be heavy on fine October days.
Spring (April–May) is also excellent. The forest is green and fresh, the weather is mild, and visitor numbers at the palace are lower than in peak summer. Bouldering is good in spring, though rainy spells can make the rock greasy.
Summer (June–August) brings the largest crowds, particularly in July and August when Parisian families use the forest as a weekend escape. The palace queues can be long; book tickets in advance. Bouldering is largely suspended in high summer — the heat makes the sandstone too slippery to work effectively, and many climbers avoid the area between June and September.
Winter (December–March) is quiet and atmospheric in the forest. The palace is uncrowded and can be visited at leisure. Bouldering conditions are excellent in dry winter weather, though frost and rain can close the circuits.