Buried man cave

[Daz140]

Hello everyone 

After finally finishing the main house we are moving onto the back garden - we have been here ten years and the neighbours have said the garden has not been useable for a further 10.

 

I’m curious what to do with this section. This used to be an avery with a walk on roof to use the garden on top. I would like it as a man cave or just a storage area. The story goes that the roof was worn so the whole thing was filled in - hopefully the birds were removed first 

 

Conveniently the neighbours were also working on their garden and had tons of blocks and soil to get rid of so moved it into what became my garden - seems to me they took advantage of the previous owner here 

 

After poking around, the side walls are solid but as yet to find out the back wall. The back wall is dug into a sloping field. If ok what roof system could I put here that  would be safe to walk on - was thinking maybe deck on top of the roof suspended between the two opposite sides

 

if the wall is damaged could a block wall tied into the sides work - drainage? My garage has a similar setup which I tanked and have had no issues.

 

We are in no rush to this project as we have a front garden we can use but I don’t want to just block this up and go over it when there is a chance to use it.

 

I understand it will cost a bit to remove all of the contents and if it’s a case of ‘get a pro in or u will die’ I will still like to see ur suggestions just so I can understand the reasoning behind it

 

Thanks 

Measurements are:

 

2.5mx3m

Height 160cm

[Nickfromwales]

Is the wall to the left (the original, shorter wall) retaining anything? Are both rear gardens at the same level? 
 

The block-work looks ok but obvs the cracked few blocks would need replacing as I bet you could just push those off.

 

My 2 cents is to demo the lot and put a nice shed there, which will have thinner walls so you’ll gain more space. 
 

Drainage? You don’t need any as it’s outside, literally, so the rain will just go wherever it wants to. If you put a shed there you just leave a gap between the shed and the walls so rain and runoff from the rear retaining wall just go straight to ground.