Your castle is key to survival in V Rising. Your castle acts as your base of operations for all your upgrades and provides protection from the blazing sun during the day. It's important to upgrade your castle heart to expand your base. Here is how.
You can upgrade your castle heart by interacting with it (press F). In the castle menu, you will see its current level and upgrade cost at the top. The first upgrade will cost 12 Copper Ingots and 12 Leather. Once you have acquired these items, you can upgrade the base by clicking the Upgrade option.
The upgrade cost will change as you progress through the various levels. You should be upgrading your castle as soon as possible, as it will expand your castle capacity. This will increase your border limit and Servant limit.
Related: How to make a roof in V Rising
How to Stop Castle Decay
Your castle will decay over time. You can stop this by adding Blood Essence to your castle's heart. This increase the time your castle will remain powered and fortified. It's important to regularly check your castle's power and time remaining before it decays.