More maps at Stanford's map page
HEPL is located in the Physics/Astrophysics Building (Varian II) at 452 Lomita Mall, between the Main Quad and the new Science and Engineering Quad
You can also take Stanford's Marguerite Shuttle from elsewhere on campus to the Panama/Ortega stop near the parking garage and then walk through the Science & Engineering Quad to HEPL.
Kistler Conference Rooms #102/103: First floor lobby, Physics/Astrophysics (Varian II) building
Conference Room #214: Physics/Astrophysics (Varian II) building, Northwest End, 2nd Floor
Conference Room #241: Physics/Astrophysics (Varian II) building, Southeast side, 2nd Floor
Conference Room #232: Physics/Astrophysics (Varian II) building, Southwest end, 2nd Floor