In reply to Removed Userchacha:
In fact the nearest station isn't Fontainebleau but Maisse, some 6 km away. Its on the suburban RER ligne D which you catch either at Gare du Nord or Gare de Lyon. But there's no bus service so you'd have to walk (quite pleasant along a GR for much of the way) or find a taxi.
But there are other campsites nearer to railway stations such as At Bourron Marlotte (information on several other threads) - these are slightly further from the climbing areas but still manageable without transport