See Ambrogio Lorenzetti’s frescoes as you’ve never seen them before! The Effects of Good and Bad Government on the City and the Countryside (ca. 1338) are truly spectacular, and you can visit the restoration site for a limited time. The special 30-min guided tours are offered 6 times a day from 1–25 June and then from 11–31 July, but English visits are only on Monday mornings (10:30, 11:15, or 12:00). If you cannot get an English tour, I would still recommend you go, as you will enjoy seeing the details of the frescoes from a different perspective, and then you can visit the rest of the Palazzo Pubblico when you come back down. Entrance times: 10:30, 11:15, 12:00, 14:45, 15:30, 16:15.
Booking: Click on "Biglietti" in the upper righthand corner of this page, then choose "Visita al Cantiere del Buon Governo". Your ticket includes your entrance to the Palazzo Pubblico/Civic Museum as well, so you can look around before or after your timed entry to the worksite. Note that the ticket option “Civic Museum” does not include a visit to the restoration site.
NB: No lift, but only about 15 steps involved to get up the scaffolding. A maximum of 9 other people will be up there with you, and the platform is the entire length of the room (squeaky, but stable!).