This is the tunnel used for the entrance to TOON TOWN in the movie ROGER RABBIT. Travel through it now and you'll get to the Greek Theatre. Over to the left of the second picture, this site was used for the picnic in BARTON FINK.
This clip from ROGER RABBIT on You Tube includes the entrance to TOON TOWN sequence. Enjoy it if you can wait long enough.
Thanks to apusama for the video.