Here's part 2 of a look at Ralph McQuarrie's concept paintings for Return of the Jedi.
In addition to scenes and locations familiar from the finished movie, McQuarrie also created numerous paintings for locations that were either ultimately unused, or used in later movies.
The above is a prairie-type environment that was a possible location for Jabba's palace.
At one point the Emperor's throne room was going to be housed on a lava planet, as shown above with Darth Vader bring Luke Skywalker before the Emperor.
Above is a view of the Imperial Palace on the capital planet which was entirely covered by an enormous city. This planet would eventually become Coruscant via the expanded universe material and would debut in the retooled ending of Return of the Jedi for it's theatrical rerelease in 1997, before becoming a central location in the prequel trilogy.
Above are three views of Monument Plaza on what would later become Coruscant. The Rock shown in the first and third views is apparently the top tip of a mountain, and the only natural feature to be seen on the planet in it's current state. This was to show just how tall the surrounding buildings had become.