I’ve had some trouble finding detailed information on this site in Jaisalmer. It is a series of old buildings, including temples near a lake in Jaisalmer. It’s a lovely spot to visit that can make for some nice pictures in the morning/evening. When I found it online it was listed as the ‘Postal Colony’. Subsequent research has found various spellings of ‘Gadsisar’, ‘Gadi Sagar’ and a few other variants. I’m sorry I can’t provide more information but you can find it in the city based on these names.

http://www.jaisalmer.org.uk/tourist-attractions/gadsisar-lake.html

https://en.wikipedia.org/wiki/Gadi_Sagar_Temple