As well as all the skill plots there are a load of other upgrade/customizations that can be done at the citadel, they require a large amount of resources but from i can see don’t require any upkeep.
Citadel Walls
- Helix, 750 Wood
- Crux, 7500 Wood
- Diamond, 15k Wood
- Bulwark, 45k Wood
- Arcana, 40k Wood, 10k Stone
- Spikes, 50k Wood, 15k Stone
- Tableau, 70k Wood, 20k Stone
- Bladeleaf, 100k Wood, 15k Stone, 10k Precious Bars
- Serpentine, 125k Wood, 15k Stone, 15k Precious Bars
- Hubris, 200k Wood, 20k Stone, 50k Precious Bars
