I thought this would be a fun discussion to have that I haven't really seen around here before. We all know the basic story. Mjoll was severely injured by the Dwarven Centurion while exploring Mzinchaleft. Aerin found her, helped her back to health, and now they're friends.

It seems simple enough on the surface, but it gets confusing when I actually think harder about it. The reason I say that is that Mzinchaleft is a fairly remote location in the wilderness between Morthal and Dawnstar. Aerin, on the other hand, can't fight his way out of a wet paper bag and strongly suggests in his dialogue that he's never really left Riften. What was he doing around Mzinchaleft, and how did he even survive such a long journey? Since Mjoll is portrayed in no uncertain terms as an honorable and trustworthy person, I'm assuming that the story is meant to be true, but it doesn't really add up for me. Is this just sloppy writing, or does somebody have a fun theory to tie this all together?

Mjoll crawled her way out. Aerin didn't go in the ruins but he was nearby... which is still odd.

Why would a Stalker with an Obsession for a Person be near enough to the Object of His Obsession to be able to aid Her if She was injured?

Mjoll was wounded very near to the exit, and even Our character should be able to use a stick to activate the Gate Mechanism.

According to Aerin, he had never ventured far from Riften which is odder still, and makes me feel a little better since I sat and watched him being murdered by a bandit near Falkreath. Should have stayed at home, or atleast upgraded that iron dagger.

He was a creep, and Mjoll is far better off without him!

So this little fellow found her near Dawnstar, and then hauled her lifeless body back to Riften? ... yeah, right.

The exit from Mzinchaleft is right next to the road. I always assumed Mjoll managed to reach the elevator, and opened the gate at the surface. Then it just takes Aerin passing in a wagon or carriage on the road.

That's what I always figured to be the case. Like the Good Samaritan, he stopped to collect someone in bad shape lying near the road.

And "Never left Riften" may refer to his place of residence. Business may sometimes necessitate traveling to other cities and towns.

I suspect he's never gone "venturing" but may well have taken the carriage you can hire to go to other cities. The in-game anomaly of being able to travel to the minor holds, but not back, can reasonably be ignored.