I stumbled some information about two interesting-sounding towns:
- Büsingen, a German enclave in Switzerland. Send mail either via Germany to D- 78266 Büsingen, or via Switzerland to CH-8238 Büsingen. Some pictures here.
- Baarle-Nassau/Baarle-Hertog, a Belgian enclave in the Netherlands. Well, kind of: there are also bits of the Netherlands inside bits of Belgium which are themselves inside the Netherlands. The boundary runs through the town and even through individual houses. See some photos, some more photos, or read a description of how the situation came to be.