Expeditions can be a major source of income if properly invested in. They can be found under the Quest section of the menu. It costs 50k gold to start an expedition. Once started, you will see four adventurers that can be leveled up different tiers of any resource for increased rewards. Sellers will have to buy resources to use on expeditions and scouts will have to sell relics to buy resources for expeditions. Other tradeskillers can simply use the resource they produce.
There are two constraints on the level of an expedition: K-level and E-level.
Means the maximum it can be based on the number of adventurer guilds your kingdom has. People not in a kingdom have a max K-level of 1, which is a reason why being in a kingdom is important.
Is the sum of all your adventurer's levels. Upgrading an adventurer to the next level will have a certain E-level requirement so some diversification in your adventurer's levels may be needed to improve one higher.
Expeditions Slots Edit
You start with one expedition slot, additional ones can be unlocked using gems up to 5 total slots. Slot 2 costs 250 gems, slot 3 costs 1000 gems, slot 4 costs 2500 gems and slot 5 costs 7500 gems + 25 miden shards. That may sound like a lot, but unlocking the slots is worth it and will pay itself back quickly.
Improving your expeditions. Edit
To do that, you need to go to into the expedition page where you send expeditions and click on permanent boosts. Here you can spend increasing numbers of resources to get upgrades to the rewards from expeditions. These upgrades require fixed types of 2 resources, but of any tier. Giving 1 T5 resource is the equivalent of 10 T1, 1 T4 is 4 T1, 1 T3 is 2 T1, 1 T2 is 1.25 T1. The major 3 boosts to focus on are gem boost, relic boost, and time boost. Key boost is also good, followed by orb boost, and lastly scroll boost. Try the main 3 to level/step 16 which would show 0.207 for gem boost, 4.134 for relic boost, and 1.653 for time boost. Eventually you will want to go higher, but step 16 is a good mid-game goal.