Simple question, no spoilers in here, just wondering how do I get back to blackreach after I've left it? If there is a way of course...

you can get back in the same way you did before

If I recall right, there was a tower in Blackreach that took you to the surface. That tower should be somewhere around the Aftland Glacial Ruins entrance. Maybe.


Or if you can't find that, you can go back into Aftland then head down to the sanctuary, and use the mechanisms that you put the circular and square keys in.

Dwemer ruin delving. You'll eventually run into a set up like how you first had.

Mzinchaleft is the easiest way.

there are 3 dwemer cities that provide an entrace to blackreach using the same method you used in Alftand with the Attunement sphere.
There's also the Tower of Mzark which is probably where you got out from and 3 lifts that must be unlocked from blackreach that will take you to the surface, and vice versa.

Only problem is, is that the towers are locked from the inside and require the lever to unlock the door. But once you open the door it'll be the easiest way to travel to-and-from Blackreach.

Mzinschaleft, Alftand, and... one other around the Eastmarch/Pale border region. They all have telescoping stairways locked with tonal key panels.