What can i do with this random concreted bit in the middle of my garden?

[tantrumtime]

This is a rented house and i assume this is the foundations of a green house, the garden is south facing and gets loads of sun so perfect for that.
As you can see, i have put a picnic bench to try and 'use' the area which has my various plants on it but its a dead area really as the weeds keep growing through the cracks and im getting sick of looking at it. I really want to get the garden sorted and want this to be a focal point instead of an eyesore IYSWIM.
I am unable to do anything too drastic as its rented but i thought about getting some sort of wood border to surround it and use bags of wood bark to cover it and then perhaps put a dining set or climbing frame on it and getting some nice pots to plants bulbs in to make it look lovely. Its not flat unfortunately, i wanted to deck it but i havent got the money to pay someone to come and level it first.

Does anyone have any better ideas or suggestions or experience of a project like this? Im clueless really (can you tell by my overgrown courgettes)

You could get some rectangular planters to put round the edge - giving a low wall effect.

You could deck it even if it isn't level - there are some deck supports you can use which have an adjustable height, so you can put them down and then adjust them to compensate for the unevenness in the ground.

Something like this www.wallbarn.com/products/roof-and-terrace-finishes/support-pads-for-timber-decking/

sorry for delay - vomiting child
Both great suggestions, thank you. Will see how much ive got to spend and work out my best option.

Build sand pit for kids?

Wood frame, line with plastic (eg pond liner) fill with sand. May need a lid if lots of local cats.

Looks nice with the picnic bench on, though. I would keep it like that, somewhere for the grown ups to drink wine