Some people plan ahead. Some people get a brochure, ponder, weigh up, mark up and book up the things they want to do and see, often months ahead.

Not that my life is a permanent drift, obviously, but it's surprising how often "Sounds interesting, that might be an idea" stays just that until it's just too late to do anything about it.So the Open House weekend this year might have passed me by (again), but for chancing upon a couple of references to particular places, at just the right psychological moment to persuade me to the earth-shattering conclusion that a weekly shop is as well done on a Friday as on a Saturday, which can then be freed for something out of the ordinary.

Like, for instance, marvelling at the monster engineering project of Crossrail, currently excavating at various places in central London and burrowing between them deep below the surface. The visit to the site of their Bond Street station-to-be started with a video presentation all about the plans and mind-boggling statistics, which are all explained on their website. But what we'd really come to see was some big diggers and holes in the ground. Health and safety being what they are, the reality that we were allowed to see was, frankly, rather limited. At each end of the station (itself a gigantic box some 35 metres down), they've built cathedral-sized shafts for the excavations, and also "grout shafts" to monitor ground movements and enable underpinning to be injected under neighbouring buildings if necessary. But all we got was an oblique view of the holes, and of some of the massive quantities of clay coming up to be taken away to form a new nature reserve out in the Thames estuary mudflats.

Just round the corner from there, by a complete contrast, is the Wigmore Hall, which specialises in chamber music. They were throwing open the day's rehearsals to all comers. I'm been to more than one of their Sunday coffee concerts, so their grand marble and Art Nouveau friezes weren't new to me, but there was novelty in seeing how the player's earnest concentration could break into good-humoured informality as notes were made and comments in exchanged in the fine tuning of the night's performance.

By yet another chance, eavesdropping in the Crossrail queue revealed that the Supreme Court building was also taking part in the weekend, but by the time I got there, the queue was round the corner, so that had to be put off until first thing on Sunday.

The former Law Lords are now set up in independent state in what used to be the Middlesex County Council building, a classic Edwardian statement of pseudo-mediaeval civic pride. But within, the Court presents itself as transparent and open. In addition to a standing exhibition on the history of the building and the institution, it's been hosting a seasonal display on Sport and the Law, which explains how law has increasingly come to be involved in sport and its controversies (though not, apparently, the complaint about the 1948 London Olympics that the commemorative stamps were too big to lick), complete with an activity room for visiting children.

On this occasion, we were allowed to see the Library, but it's also possible for the public to visit the building's exhibitions and attend hearings the rest of the year as well. Some of the old civic chambers are used as courtrooms; when they're acting as a final court of appeal for those Commonwealth countries that still use the Judicial Committee of the Privy Council, they sit surrounded by grand panelling and ceiling beams. But when meeting as the Supreme Court for the UK, they use an austere modern room, not under a Royal Coat of Arms, but under a purpose-designed emblem symbolising each of the countries of the UK, enclosed in a stylised scales of justice and an omega;