so i build a celler and theres like a door way arch in the celler but theres a brick wall blocking it so you can step under the arch and go no further ??

how do i build the secret tunnel or what ever this archway is for ???

vampire lord or vanilla skyrim vampire ?

Considering the coffins come from Dawnguard if I remember correctly, I think you at least need that DLC.

Don't know for sure though.

both.

You probably need DG, not sure. Alva has a coffin in her basemant.

i doubt you need DG just to get the coffin normally Dlc′s dont interfere with other Dlc′s but i maybe wrong there is only one way to test it...

You need to be a vampire for the option to be available at least, do not think dawnguard is needed

I'm pretty sure that you do need DG for the coffin to be an option. It's a special texture that only appears in dawnguard, not the flimsy wooden ones from vanilla Skyrim. Also, as a PS3 player who got all the DLC in the opposite order I had to deal with no Stahlrim arrow crafting in DB so the DLCs do interact a little, but never backwords like planting ingredients from Soltheim in your garden. (At least I think so.)

Tip for non vampires: Take the oversized Stahlrim disposition sorce map you get off the bandits corps and slide it into the archway. It just so happens to fit perfectly and now you have a momento from your trip to Solstheim to keep on display.

So that's what that alcove is for! I always wondered about that.