Cheers was filmed on Stage 25 at Paramount Studios in Hollywood.
The set was designed by Richard Sylbert. It was patterned after the Bull & Finch bar in Boston. But the B&F is much smaller, and the bar itself is up against the back wall. The decor, Tiffany lamps, and stained glass is true to the B&F.
Director James Burrows had a lot of input into the design which is why it was so easy to shoot in it. You could bring cameras way up into the set, get many different and interesting angles, and even get shots all the way down the hall.
If you look closely you’ll notice a line that runs down the center of the bar. It’s on a hinge and actually the right half can swing around, allowing room for the right wall to swing back revealing Sam’s office.
If you look closely, you can figure out how the wall moved:
Now check the angle between the wall and the stairs when filming in Sam's office. Then check out the bar scene:
The third wall of Sam's office is not shown much in the series. Here's a glimpse of it:
Here's a scale model that explains everything:
Miniature set designed by Charles Brogdon. Check out his flickr page for more!