The Mae Sa snake farm of Chiangmai was where John Rambo was employed for an unspecified number of years as the snake catcher.
It was signifigant because it was a real business and the only known instance where John Rambo has been seen working for money at a job. The owners are very proud to have been featured on a popular worldwide film and have signs around the business about how the movie was filmed there.
John Rambo is seen working at the farm by catching snakes in the jungles of Thailand. He travels back on the Salween River by his boat, which he also uses to catch fish and give to Buddhist monks, presumably from the monastery he lived at during the events of Rambo III. Rambo returns to the farm and takes care of the snakes in their cages as well, feeding them mice and making sure that they have plenty of water. Rambo does not seem to like his boss, however, and the two don't get along, primarily because he wants another python and they already have too many cobras. Rambo replies in English for the owner to "fuck off", and the owner presumably does not pick up on this, as he may not understand much English. Rambo is later encountered at the farm by the missionaries from the Christ Church of Colorado, who ask him to transport them into Burma on his boat.
Rambo also has a small shop on the farm grounds where he does metalworking, primarily forging. He is seen in this workshop forging a new propellor for his boat and a machete. Rambo possibly lives in a small hut located on the grounds, and likely does. He also keeps his boat docked near the farm.
The farm was a real establishment and not just a film set. The deejay who announces the snakes and how dangerous they are was a real person and is still employed there to this day. His name was Mr. Wasawat Panyarat. The snake fighter was also an employee and his name is Mr. Kammul Kawtep. The cobras seen in the film are real and venomous, so the snake fighter was in real danger and not just an actor for the film.
The farm is now a popular tourist spot and is doing very well financially, although snake farms have come under fire by some animal rights activists who claim that exploiting the snakes is harmful and stressful to them.