When I was a student on the Vampire at Valley in 1961 the boss of Ground School used to take us on hikes around the wrecks in Snowdonia. They were all plotted on a large scale map in the HQ of 22 Squadron so that they didn't have to scramble a helicopter every time a member of the public reported finding a "crash".
I can remember a Douglas Havoc and a Lincoln in particular. There was also a tantalising tale of a intact Swordfish which was supposed to come out of a bog every ten years or so but I never got to see that.
I think the Dakota wreck that BEagle refers to is that of EI-AFL of Aer Lingus which struck the top of Snowdon on a flight from Dublin to Liverpool (or vice versa) on 10th January 1952. The aircraft went into a bog near Llyn Gwynant pretty much in one piece. Only the tail and the tip of one aileron was visible - the rest of the aircraft was in the bog.
We were told that the rescuers had only been able to recover the body of the stewardess from the back of the fuselage - everyone else was still in the aircraft. A fence was erected around the wreckage and the land inside was declared consecrated ground.
Legend had it that the RAF had tried to get the aircraft out using a Coles crane and that the crane was now also in the bog!
I seem to remember that we walked out at a little place called Roman Bridge on the B498.