These three worlds were generated in September 2014 after the eve of the Terraria 1.2 release.
The idea behind these servers -- since mediumcore and PvP are forced, as well as player logout (exit) positions are saved -- is that there is some inherent competition for positioning which allows things like castles, fortifications, as well as general destruction of these things, to be useful.
Of course teaming up is a viable option that allows for towns to generate resources as well as power in overcoming a formidable foe. Such as that goes, I created a castle that I barred up with crimson rock (whatever it is specifically called) to keep some people out, and stored various resources there.
In this way, it adds to the dimension of the Recall Mirror in order to return to town quickly in a need to defend it.
Currently only Birsford is populated with structures, and the other two servers have been untouched.
The server IPs/ports
If the numerical IP does not work, try the name:
IP: open-c .dtdns.net
in place of the IP in Terraria
I've been noticing, people are trying to join the servers, but are being kicked due to not joining with a
mediumcore character -- you have to create mediumcore character first, and then join with that character.