You can configure it statically but there used to be the anycast address 192.88.99.1 and the idea was that you'll get routed to the nearest one by magic of BGP. It was retired once native IPv6 deployment took off.

Apparently the practical problems were related to people haplessly firewalling it out (ref. https://labs.ripe.net/author/emileaben/6to4-why-is-it-so-bad...)