I live in the San Francisco Bay area, a center of varied geology and significant geologic history. If you travel enough, one day you'll be laid over in some airport city for a day. What if it were here? Sure you could party with local friends, but you could also take those friends with you on a field trip!
Now I could make a huge list, but it's easy to find on my site and I'll spare you. I think it would be more interesting to know about YOUR city. Post a comment or submit a post to the collection.
(Oh, OK, here's my California Geology stuff.)

Comments
For very short layovers, have some science in the airport!
Adelaide, Australia — catch a bus south towards Flinders University, and walk into Sturt Gorge, which is the type locality for one of the Neoproterozoic tillites which form part of the evidence for Snowball Earth (see http://www.ajsonline.org/content/300/5/347.full.pdf Table 1 #39)
Oh, Andrew, joy of my heart, I have just the thing: http://freethoughtblogs.com/entequilaesverdad/2011/12/21/layover-geology-discovery-park/. And soon more where that came from! Thank you for the meme – this is going to be outstanding good fun.
Layover short, don’t miss your connection — take a cab down town and look at what the building, banks and churches, are faced with.
Oh, Andrew, I read the headline of the post quickly and at first thought it said What’s a Good Field Trip for a Lawyer? I envisioned various scenarios involving high cliffs in uninhabited areas, but couldn’t quite connect it to geology…until I read it again. Sigh.
I like David Beatty’s suggestion. In fact, various geology classes at San Jose State University, which is right next to the downtown section of San Jose, do short walking tours looking at the facings of some of the more geologically decorated buildings. If you called the department in advance and got them to fax you the Walking Tour worksheet, you could do a 20-minute cab ride and see a whole variety of interesting facings. Downtown isn’t that far from the airport, as I am reminded every time a plane lands.
Auckland (New Zealand) has 50+ small volcanoes within the city area – several are within walking distance of the airport
Recently went on a field trip sponsored by AEG in Vicksburg, MS. They had two retired geologists from the Army Corps of Engineers facility there who co-narated the excursion. One covered the geology and the other the Civil War Siege. The lesson was how geology influenced the siege. They produced a small guidebook.A short ride from the Jackson, MS airport.