In the beginning, the car ride of Mark, Elizabeth and Rachel is filmed on South Main Street in downtown L.A. At some point you can see the intersection with 6th Street (street sign and stop lights visible). One of the buildings in the background in a close-up of Rachel on the back seat (seen though the car’s back window) is the Cecil Hotel.When Elizabeth gets off at the ER exterior set and when Mark continues to drive past the hospital exteriors on the WB lot, the intercuts of Rachel inside the car are from South Main Street also.Carter and Susan's yoga class is filmed in a room of what used to be the Los Angeles Design Center, historically (and nowadays again) known as the Title Exchange Building at 433 South Spring Street, L.A. What gives it away is the elaborate doors inside and the sort of crossed bars in front of the windows, which are typical of this Art Déco building. It's been used in hundreds of productions, and I was there once because it was also a filming site of "Falcon Crest". Sorry to say that this particular room was not among the rooms I visited in that building, so I can't tell you the room number or which floor it was on. The building underwent major renovation recently.