Rule vault is one of the towers that you CANNOT upgrade. Here, you can view all your runes or salvage/upgrade them.

Depending on your forge level, you can forge different spells, boosts, and timers. You can also purchase timer packs, war packs, for rubies. This is an upgradeable building.

Breeding Castle is where you can view your dragons lineage starting from red to Verdant. You breed dragons here during breeding event. This is an upgradeable building.

Team Hall is the other building you CANNOT upgrade. This is where you can access team wikis, check your status, and search for other teams.

Your egg incubator incubates your eggs. This is an upgradeable building.

Builder Hut is where your builders live. This is an upgradeable building. To upgrade this, it will take wood and EGGS

This is where all your food and lumber (rss) are stored. To gain a higher capacity, you must upgrade it as you level up. This is an upgradeable building.

Research hall comes with benefits depending on what you research. You can research by spending extra eggs. This is an upgradeable building.

Bounty Harbor gives you prizes every 24 hours. If you miss one day, you will have to restart at the beginning of the list. This is not an upgradeable building.

If you complete a certain quest, you will receive egg tokens (or depending on your balloon level, you will receive timers). This is an upgradeable building and will costs eggs rather than wood.