Some years ago I flew from one of the few totally grass RAF airfields, which was temporarily closed and ATC unmanned. A light aircraft appeared overhead, let down and landed, then taxied in and shut down. The pilot then tried to get into the locked ATC tower. OC Flying (wearing RAF uniform) walked out to talk to him. On being asked why he had landed at an RAF airfield without clearance, he said he was on his qualifying solo cross country flight. When asked where he thought he was, he gave the name of another airfield. OC Flying pointed out the ten foot high white lettering on the adjacent hangar which said "RAF *******". The pilot disagreed, as far as he was concerned this couldn't be an RAF airfield! He was asked what type of surface he expected to land on and he said tarmac. He never noticed it was all grass here.
He also demanded that OC Flying signed his logbook so he could get on his way. His flying club were soon contacted and asked to send a responsible adult to fetch him back!