Edit 24 June (later): It’s back up now, and now in Tampa, Florida.
The server crawl.s-z.org will be down for a data center migration most of Sunday, 23 June. If you’re looking for another US server, you can play on crawl.akrasiac.org instead.
Edit 24 June: The ISP had various problems with the move, so cszo is still offline. I’m in contact with them to get the remaining issues resolved.