The first thing that comes to mind is an ice skating rink. Haha. I can't imagine what someone had in mind when they built this. Seems too large for fire pit unless bonfires or something like that. Need a swimming pool? Seems large enough to handle one. But it does not seem to invite some big view or wall obstructing planting scheme.

I think a larage firepit with curved seating along the curved wall and the some moveable seating around the rest. Is that space actually level it is hard to tell from the pictures.I am wondering why such small decks off the house the one on the left could have been a huge multi level useable deck and all those bits of deck joined together to make an amazing outdoor area .

We do not have enough info.

How many people live in this house and will utilize the outdoor space?

Kids?

Senior citizens?

Is it your desire to keep some/all of the retaining wall?

Does this yard face east? It looks like it's mostly in a shadow per the pics you took.

What zone are you in?

Is access to this yard easily accessible?

What IS your budget?

some ideas:

I would be likely to plant deep shrub and flower beds along the curved walls and have a seating area, either a masonry patio or a flat grassed space in the center. But I am more interested in gardens than a fire pit, and with the woodlands in the background I certainly wouldn’t want a fire pit so large that the walls would be good seating distance away and with flying embers.

So how you envision using your yard is important as Janie Gibbs mentioned.

so think about:

kids’ play space?

veggie or ornamental gardens?

adult place space such as badminton or boules?

bugs necessitating screened seating areas?

do you like working outdoors vs. low maintenance?

Is this a year round or seasonal residence?

do you need to solve this now or can you seed it with conservation mix and wait to see how you live in the space?

You say you don’t want ‘another mortgage’ spent on this area, so my idea might be out of line.

I’d remove the far wall and rebuild it much closer to the first. Arranged so that a fire pit in the center of the two makes sense. As it is now, it doesn’t.

Play area for the kids with a sitting area for you to watch them?

You will never regret spending money on a landscape designer. Hire someone who will work with you and provide a plan that can be executed by professionals or by yourself. A plan that stipulates materials for paths, lighting and plants. A plan that can be done in stages if that is better for your budget.

In our first home when budget was a big issue we used a designer who provided a plan that we executed. We’ve followed this format in subsequent homes although now we can afford to pay a landscape contractor to execute the plan.

Good luck.

How about another Stone Henge?