The velodrome

I'm in London for a celebration of the life of Adrian Cave. It took place this afternoon in a large lecture room, part of the recently-opened Oil Tanks at Tate Modern. One of Adrian's last projects, he helped in designing its access with elegance, much recalled as his thing at the packed meeting. Its affectionate spirit was summed up by a grandchild's quite brilliant "performance" of Albert & the lion.

The gloomy Oil Tanks themselves were showing video instalations, the magic of which continues to elude me. No doubt I suffer from late onset ADHD.

Before leaving Bankside, I sampled Tino Sehgal's Unilever Series effort in the Turbine Hall. You hardly expect to see two-dimensional framed pictures in that giant space, but this "show" is the exact reverse of what one gets in a conventional gallery. It's a Whiteread experience.

A room full of Rothkos, for example, sees people looking at the walls in silence: Sehgal has us standing or sitting in the Turbine Hall, looking at one another: "us" includes Sehgal's animators, who are liable to come up to one and engage in random conversation. Thus I had the joy of discussing sea bathing off the English coast with an attractive young lady, who broke away as suddenly as she first approached me, only to go and stand 20 yards off. I waited where I was a little longer, wondering whether I was now entitled to walk up to someone in my turn, and what I should say; but I became distracted by the realisation that the Turbine Hall floor would never quite recover from being dug up by Doris Salcedo for her 2007 Unilever show.

En route from Paddington, I paused by the Serpentine Gallery. This year's Pavilion is another sombre affair: a subterranean chamber, with stepped seating finished in dark grey cork to match large mushroom-shaped stools which comprise the only other furniture. The "space" is covered by a flat disc, its surface covered by an inch or so of water. Eleven of the columns below the disc are supposed to characterise each of the eleven previous Serpentine Pavilions, but you could have fooled me.

Avoiding buses because I feared Olympic traffic congestion, I have been riding a Boris Bike for the first time. The sponsors' name has attracted the odd graffiti artist, as can be seen from my photograph. Renting is easier than in Paris, but the biking isn't such fun, certainly when rounding Parliament Square and crossing Westminster Bridge - a bit hairy, dicing with all those buses. Even on the bike route through Hyde Park, it was tricky, being so hugely busy: in Beijing (according to our friend Edward, who came to see us the other day - he's been living there), people are moving from bikes to cars, in London it seems to be the other way about.

The Boris Bikes are low-geared, so it's warm work on a day such as today has been. I arrived at the Albert Hall from Bankside very hot and sweaty just in time for the Prom, and - standing in the packed Arena - spent most of the first half mopping my brow. It was the great B Minor Mass: the Guardian critic gets it just right - four stars. "When counter-tenor Iestyn Davies sang his solos," he writes, "his extraordinary tonal richness and imaginative phrasing combined into something truly unforgettable."