Where is the Ark of the Covenant?
The most important person as far as the Ark of the Covenant was concerned was Moses, who had it built to contain the stones with the commandments carved on them, which he had brought down from the Mountain, and kept as a sacred relic in the tabernacle built for the purpose to keep the Ark in it through the crossing of the desert for 40 years.
There was nothing Moses wanted the most than to see "his" Ark in a sumptuous Temple built for it in the Holy Land. He wouldn't because he had to die before the People crossed the Jordan into the Holy Land.
Then, the Law, the most precious content of the Ark became a sysnonym with Moses himself, as Jesus himself was reminded of as he proposed the parable of the Richman and Lazarus, that if the relatives of the Richman in hell did not listen to Moses, i.e. the Law, even if one was raised from the dead, nothing would prevent them from ending themselves up in hell. (Luke 16:29-31)
Now, when the Babylonians destroyed Jerusalem, the Ark of the Covenant was no longer in the Temple. What could be the most logical thought to come to mind? That the Prophet of the time, Jeremiah, must have had a vision that the end had arrived for the Temple, and that he should do the only right thing that was supposed to be done, which would be to return the Ark to Moses.
Between Jericho and Jordan there is a great mountain called Nebo, whose highest spot was the top of Pisgah, wherefrom, Moses was allowed to contemplate the Holy Land that he was not allowed to enter. There, on the Mountain Nebo at the top of Pisgah, Moses was to die and be buried. Whoever buried him must have kept the secret till death, because up to this day nobody knows the place of his sepucher. That's where Jeremiah took the Ark of the Covenant to. He must have had a vision about the place and buried the Ark where Moses was supposed to be. That's where Jeremiah hid the Ark of the Covenant: In the hidden sepulcher of Moses. (Deut. 34:1-6)
In conclusion to this thread, if you compare Deuteronomy 34:1,6 to Jeremiah 3:16 the verbiage Jeremiah uses follows the same pathern to the secrecy stipulated with reference to the sepulcher of Moses, to be kept out of the popular attention. I see here an extra evidence that Jeremiah, by means of perhaps a vision, had found out the hiding place, added to it the Ark of the Covenant and perpetuated the secrecy. None was supposed to know or even remember that one ever existed.
Ben