Arguably the only unique tile improvement that can compete with the Scottish Golf Course for the title of "the worst unique tile improvement in the game", the Kurgan's usefulness ends as quickly as it is unlocked. It can almost be used well for one purpose and one purpose only: to get a Pantheon without having to run the God King policy card, and that is pretty much it. Both the Faith and the Gold output on this improvement are abysmal. Gold is slightly more useful for Scythia as a Domination civilization, especially when we consider that Scythia will field a massive cavalry army, but a Kurgan only provides 1 Gold, and scales so poorly with further technology research and it can never be a decent source of Gold to pay off the maintenance cost of units in any era. And if you play Religious Scythia, which is possible, you will still have to rely predominantly on your army and conquest for religious conversion, and Holy Site districts and buildings for Faith, since there is absolutely no way this improvement alone can supply enough Faith to pay for the ever-increasing cost of Missionaries and Apostles. Not to mention, for an improvement that does not provide Food, Production, Housing, or any yield that is large enough to be meaningful to the civilization's preferred Victory path, it will be a huge burden for cities if you build too many of this. All in all, just one Kurgan, two if you really want a fast Pantheon, and then you will be better off saving those flat land tiles for Farms. This improvement should only be built on Desert or Tundra where Farms cannot be built (which is pretty weird in itself why Scythia would settle or keep a conquered city on these terrains since they cannot make those cities very bustling or productive), or on tiles adjacent to at least 2 Pastures, because otherwise, it is a waste of a Citizen that has to work an improvement that only provides 1 Gold and 2 Faith.
For some reason, some of civilization’s greatest feats of engineering and construction are mausoleums and tombs, and, for some reason, these great piles are usually reserved for military and political leaders. For the Scythians these piles were great mounds of dirt, now called kurgans, from the Turkish word for “mound.” It appears that a number of the barbarian nomads of the steppes of Central Asia began interring their leaders in these mounds sometime around the 4th Century BC. By the Early Iron Age, the kurgans of the Scythians and other tribes were truly impressive mounds, some as much as 500 meters (1600 feet) across at the base, and might stand as high as 27 meters (89 feet). So, these tended to stand out on the rolling open terrain of the steppes. And then the Scythians decorated the tumuli with the bodies of slaves and horses, just to insure it got everyone’s attention that here lie a great man (or perhaps woman).