From what we've found on the Chaos discord.
Castrum spawns 100% of the time when you have a party or parties of rank 10s and it spawns after an hour of the instance being open.
Castrum also rewards a 'maximum' of 26 coins per run. With a minimum of 20 for a full clear.
If you want full haste gear farmed ready for 48 man savage in 5.4, You need 2600+ coins.
You're looking at over 100 runs, (assuming you get unlucky with the 3% drop rate augments in Castrum bosses).
I love a grind, I come from older mmos, but this is a little tedious. It took me 5 hours today, to get 76 medals. Not including the fact I was not selected for an instance.
It would not be so bad if Castrum spawned after 15 minutes. Please Square?
I like this content, I love Eureka, love BA and I'm looking forward to day 1 progging savage when that's out.
But please, make the grind a grind, just not something so achingly tedious please. It genuinely is normal tier difficulty and can be brute forced with rez mages, so I don't see why it's walled behind an hour long timer. Please square.