Was the great escape true and how many escaped?

Yes it did the films (The Great Escape 1963 and The Wooden Horse 1950) were based on books written by former prisoners. The camp was Stalag Lufte III Permanent Camp for Airman No 3) and was located in modern day Poland. Despite the escapes the camp was actually designed to make tunneling difficult. The accommodation was raised off the ground to make it easier for the guards to see. The soil it was built on was very sandy making tunneling a dangerous occupation as the soil would need supporting and also the colour of soil would easily show up. In addition seismic devices were planted in the ground to detect tunneling. The first escape in October 1942 was done using a version of the Trojan horse theory taking 3 months to complete with little shoring up and the use of the Wooden Vaulting horse disguising the sound of tunneling. Air holes were poked through the soil to provide air. The horse took the men, materials and soil backward and forward each day. The 3 men all escaped and made it back to the Britain. The Great Escape shown in the film happened in March 1944 having been planned first in January 1943. It consisted as per the film of 3 tunnels Tom Dick and Harry, Tom being discovered by the Gestapo. The tunnel (Harry) finally used was short and had a frozen cover. 76 escaped before the 77th was spotted. The coldest March on record for 30 years proved problematical for the escapees who missed trains and were forced onto the roads. 73 were recaptured 23 being returned to camps and 50 executed on the orders of Hitler. Only 3 made it to safety