The great Mongol rulers have left for posterity a mystery that fascinates archaeologists and historians, that of the exact location of their tombs.
Perhaps the most prominent case is that of Genghis Khan, whose zeal in keeping his final resting place hidden remains a secret to this day, despite the efforts of researchers, possible discoveries (of course not in China) and the most advanced technologies. employed in the search. The last attempt a few years ago, using satellites.
There is no documentary source, not even legends, that can provide any clues on the matter. But in other cases they do exist, although the de facto result has been the same, perhaps due to a lack of interest in unraveling the mystery.
This is what happens with the tombs of Hulagu Khan and of his son Abaqa Khan . It is known from sources that they were both buried in 1265 and 1282 respectively, in a fortress (or rock mass) on the 300 meter high cliffs of Kabudi Island (formerly known as Shahi), in Lake Urmia.
This lake, which today is located in the Iranian Azerbaijan, to the northwest of the country, was at the time of its greatest extension (5,200 square kilometers, 140 kilometers long by 55 kilometers wide) the largest salt lake in the Middle East, and the sixth largest in the world.
It contained 102 islands, most of which are no longer islands because the size of the lake has shrunk to 10 percent of its former size, mainly due to damming of the rivers that fed it and exploitation of water wells in the surroundings.
Despite its declaration and protection as a natural park by the Iranian government, and its inclusion as a Biosphere Reserve by UNESCO, they have shown signs of recovery in recent years.
The second largest of all the islands (today connected to land by desiccation and converted into a peninsula) is precisely that of Kabudi, which is also the only inhabited one, in which there are four villages located on its north, east and south coasts.
As we said, this is the burial place of Hulagu Khan and his son Abaqa Khan, according to tradition and sources. Hulagu was one of the grandsons of Genghis Khan, who became the first khan of the Ilkhanate of Persia, already established as an independent kingdom from 1259. Hulagu, who was a Christian, would go on to destroy Baghdad and take part in the Crusades. 
At his death he would be buried with all his fantastic riches, his funeral being the only one in the history of the Ilkhanate in which human sacrifices were made, since his concubines were buried alive with him.
In the nearby town of Maghara, where Hulagu founded the observatory in which the famous astronomer Nasir al-Din al-Tusi worked, who resolved the incompatibility between the Ptolemaic model and Aristotle's theory of the movement of the planets, there are several towers Funeral homes that since ancient times have been associated with Hulagu's family (specifically with his mother and sister), although there is nothing to prove it.
In Kabudi, investigations were carried out in search of the tombs of both khans in 1939. Colin Thubron recounts in his book Shadow of the Silk Road that such surveys revealed absolutely nothing, although the archaeologist in question heard of a series of cisterns and rock-cut chambers in a nearly inaccessible mountain near the west coast of the island. But he never came back to explore them.
Roger More Nisbett explored the area shortly before the fall of the Shah of Persia and the rise to power of Khomeini, which led to the closure of the country to Westerners. He found the rock-cut cisterns and chambers, but unfortunately he did not have the proper equipment to carry out an excavation. In them he found ceramic fragments that he took to the National Museum of Tehran, where they confirmed that, indeed, it was ceramic of Mongolian origin.
He was also unable to return, due to the political situation, and it seems that since then no archaeologist has returned to investigate the area.