I have been awed today by Tate Modern. As ever, Bridget Riley was inspiring, although there were only four pieces. Although Riley's best known for her op-art, what I feel makes her (later) work really special is her use of colour. She has a way of bringing out incredible beauty from a tiny palette and her choices make even her greys luminous. I also saw my first Mark Rothkos and finally understood what I've been missing: I've never seen the internal experience of colour and light captured so well on canvas.

The gallery itself is in the old Bankside powerstation. The open volume inside has been maintained with the collections housed in three galleries which feel like an afterthought on one wall of the vast Turbine Hall. The Hall currently holds a Louis Bourgeois special exhibition, and I've never seen art this big. Three towers admit one or two visitors at a time; I felt the potential growing as I walked up the open spiral staircase (or that could have been vertigo), and at the top, as I sat on the chair with the huge curved mirrors around me and the other people watching from the balconies and higher levels, as I sat, offered into this space, I felt utter elation. There is no shame in being presented. I was conscious of my self and completely at ease.

The Turbine Hall was the only area in which I could take photographs, and I can barely wait to have them processed.