Retaining wall extension

[Welshii90]

Me and my partner have moved into our first home during the pandemic. Our garden is built on a slope with the house being at the lowest. Outside the back door is a concrete area that has a cinder block retaining wall with step to the side leading up to the rest of the garden. I am looking at extending the downstairs to the concrete area and want to know if it possible to extend using the retaining wall adding a second skin inside without having to dig up the 5ft deep compacted earth on the other side.

 

[kingandy2nd]

Probably not. Damp for starters, unknown quality of the current wall or its foundations as well, but practically how would you have any windows or doors in it if partially underground?