I haven't understood how the Mythic dawn were able to get a map onto a tomb in the imperial city to their location. I really don't understand. Was it placed there before? Is it just some unanswered question? Does anyone know?

There are multiple Mythic Dawn agents in the Imperial City. One of them put it there, I'd assume. How? Magic.

Well......yeah. I guess that makes sense. It just didn't make sense to me for a while.

Once you reach a certain point in the main quest you can't rest for an hour in the Imperial City without being jumped by at least one Mythic Dawn agent. I'd have to consult a wiki to get the exact number but there's at least four agents there in the game, and in the actual lore probably dozens or hundreds as the population of Cyrodill is scaled down a lot in the game from what it would really be like for hardware reasons.

In fact there's a book in the game that tells how Oblivion Gates are opened, and there must be a mortal agent present at the opening of each one. The ritual takes at least a full day, and there's a mortal on one side and a Daedric sorcerer on the other both working together to open a stable portal. There are at least 60 Oblivion Gates that open in the game, and that's also scaled down. There would have to be a separate Mythic Dawn agent at the location of each one since many appear at once. There are likely many, many Mythic Dawn agents who are implied to exist who never reveal themselves.

Plus keep in mind that during the main quest, as you are collecting the 4 Commentaries books, you learn that Mankar Camoran was a contemporary of Tiber Septim. So he has had 400 years to plan this. That is plenty of time to set this up. For all we know the prince whose tomb it is might have been in the Mythic Dawn!

Nothing strange about that. All you need to do is a bit of reconnaissance

It's highly debated whether or not Mankar Camoran was actually contemporary with Tiber Septim or if Tar-Meena was just a bad scholar. Probably the latter since it took her days to figure out how to read the first letter of every paragraph of the four volumes. http://www.uesp.net/wiki/Oblivion:The_Refugees points to Mankar being the son of the Camoran Usurper, who started his invasion in 3E 249, over 200 years after the death of Tiber Septim and 200 years before the events of Oblivion.

I believe Tar-Meena is the only one to ever claim that Mankar Camoran was contemporary with Tiber.

That book is the only thing that claims he is not contemporary with Tiber, so again, you have one person - the author - saying otherwise. However, I think it is more a case of Bethesda being sloppy and not having an editor more then anything else. No one at Bethesda ever bothers to look at the lore books they write and make sure they are consistent. Not even in the same game, let alone across games. The Refugees is a great example, as it leads us to believe that an Altmer baby is born from a Bosmer mother (and presumably a Bosmer father, as I have not seen anything saying Camoran Usurper was an Altmer). So as with so many other parts of their lore, you have to choose what you want to ignore. I choose to go with Tar-Meena.

Finding the Mythic Dawn's secret shrine is considered to be a part of the initiation ritual for those who want to join the group. It makes sense that you have to do it in the Imperial City, considering how you're accepted into the Mythic Dawn by means of a secret meeting that occurs in the city sewers.

The map was placed there a long time ago when the tomb was built. It's always used as part of the initiation test, not just for this time with the player, so we can assume all the current acolytes at the Shrine found it before.

The effect happens every day, regardless of whether you read the books, it's only the combination of all the clues that lets you know you need to go where the map indicates to join the MD. The IC citizens will have seen the map light up, but would just think it's connected with the occupant of the tomb in some way.

Delete post. Read the post wrong.

I think that a little Bosmer as a end boss isn't that... appealing. But it is also HIS paradise, who he can be whoever he wants to be. Still, it doesn't explain why he's an altmer in a certain cavern,

The Refugees is a story, not a historical text. So I wouldn't trust it either.