Any of these?
Chelsea Physic Garden
Regents Park for the rose garden and St John’s Lodge garden.
Leighton House and Samborne House in Holland Park.
The gloriously bonkers cast courts at the V&A.
Handel / Hendrix house in Brook Street, Mayfair.
City churches (google Friends of the City Churches for a list via their church finder link). There are some gems there.
Lunchtime violin recital at St Brides in Fleet Street next Tuesday.
Museum of the Order of St John, Clerkenwell / Farringdon.
You can book tours of the conservation of the north wing of St Bart’s hospital historic buildings.
If you find yourselves near the Barbican, Postman’s Park is worth a look.
Dr Johnson’s house in Gough Square near Fleet Street.
Dickens’ house in Doughty Street near Russell Square.
Walking through the Inns of Court: Gray’s Inn, Lincoln’s Inn (if you can get on a tour to go in the library, it is gorgeous), Middle Temple and Inner Temple. Temple Church is in Inner Temple, but check opening times.
Great views from the Monument (only 311 steps to the top!) and the IFS Cloud cable car (terrifying) across the Thames between Royal Victoria DLR and Greenwich.
Pie and mash in Greenwich.
Thames Clipper boats up the river.
If you have time, Eastbury Manor (National Trust) in Barking is a Tudor domestic manor plonked in the middle of suburbia.
Have a fabulous time.