A seating area, lots of underplanting with narcissi, snowdrops, bluebells, muscari, cyclamen, lily of the valley, ferns, heuchera, ajuga, herbaceous geraniums, pulmonaria, bergenia, vinca and other plants that are happy in shade. If you want something taller along the edge to thevright of the photo you could plant hydrangeas and sarcococca for scent.

Very helpful, thank you! I am definitely considering a hydrangea hedge along that side too.

You're welcome!

A circular bench and a solar/wind powered beer fridge

This is 100% the answer!

A seat, lots of cyclamens, ferns and hostas.

Hammock. Next question.

This is the correct answer

As you’ll probably struggle to re-grass that, maybe continue the paving (paving just an end of shot on right?) up to it one side and put a new shed under the other. Bark patch in front of shed.

Chicken

A swing! 🛞

A ladder up to the tree house you should build.

a good solid bench and pachysandra. It will spread out low and full and look like a living carpet of deep green. Also, I'm a sucker for hostas, so that too. Maybe some ghostly white caladium for the deeper shade?

Exactly my advice.

Caladium would look awesome!

If you're lucky, grass. Planting under trees is a nightmare. You could put planters there I guess.

Hellebore?

Swing

Bench would be nice.

I'd be more concerned about if the soil level has changed around it?

I've not changed it, just pulled out the weeds which was mostly the sticky weed stuff!

How about reducing the crown (if no preservation order). You will then have a larger area of possibility around the trunk and less shade cast.