Stadium/Chinatown has a few nooks that were later closed to the public and are now used as storage or offices. The Beatty Street East walkway is a classic. Unless you walk to the Lost and Found you'd never know it was there.
I do however know that as late as September 2010 there was still what remained of the Dunsmuir Tunnel visible in the excavation pit of the highrises now above the Costco. I'm not sure if they've since backfilled the rest of the tunnel under Beatty Street or the cavity is still accessible within the building for inspection purposes only. It would be rather dumb to leave a massive void that big under the road and completely sealed off.
Original photographer unknown.
Linked, because they're massive images.
http://i40.photobucket.com/albums/e2...N/34f720dd.jpg
http://i40.photobucket.com/albums/e2...N/4a6be2f6.jpg
http://i18.photobucket.com/albums/b1...platoscave.jpg
I've never seen it myself, but rumor has it that Granville station has a second access tunnel somewhere. I have clue no where it emerges and no way to confirm this besides a photograph.
"Driving Skytrain Access Tunnel 25 Meters Below St. Regis Hotel
Granville Skytrain Station
Vancouver, BC"
Image courtesy of BlastingConsultants.com