A few questions:

If indeed that is your cleanout, it has to sit lower( sloped downward)
than the pipe that leaves your house. That will give you an idea how
deep in the ground it is.
When the last visible pipe leaves your house, where is it in relation
to the floor? Is it a foot below ground, above ground?
And also how far away is the cleanout and the pipe that leaves the
house?

If you cannot get the cleanout opened, is there a way to put in a
cleanout in the pipe leaving the house so you don't have to go through
that trouble with the concrete?

Do you have any problems now that you must get it opened? If not, I
would just leave it for now.