I need a south London 'experience' suitable for an 80yo man

[KatyMac]

My uncle- he likes chess, legal stuff, piano music!

He is relatively fit but 80 so nothing heart racing

Ideally before Christmas and preferably happening in Covid times

There is usually an enormous chess championship the first weekend in December in London... tickets would be amazing to that...but I think all chess has moved online only until 2021 at least

They often have lovely concerts at St Martin's in the Fields, piano recitals, choral works etc.

Kew Gardens (though I apologise as I'm not sure exactly which part of London Kew is!)

He did play chess seriously and used to be ranked

Everything is bloody closed

He regularly goes to Kew so it wouldn't be a treat

Royal Air Force museum?

For next year then, what about entering him into the London chess championship? They have different rated categories, plus open (like amateur) side competitions.
And get some tickets to the talks/events too?

A family member took a group of us to the Shard for a significant celebration - tickets to the viewing platform, then lunch in the restaurant on the 30-something floor. It was a great day out. Even if the platform is closed due to COVID, the views from the restaurant were fantastic and it was a luxurious experience. Not cheap, but memorable.

The Shard restaurant had musicians playing traditional Chinese music on classical Chinese instruments, so it was cultured if not quite piano music.