NASA Photo ID: 108-KSC-69P-335 - 69-H-786
Date: May 16, 1969

Apollo 10 astronauts John W. Young, left, and Thomas P. Stafford, prepare to enter command module mission simulator today within the Kennedy Space Center's Flight Crew Training Building. While they were practicing aspects of the upcoming lunar orbit mission, crewman Eugene A. Cernan used the lunar module simulator within the same building.

Source: NASA photo in my possession