Completing Voyages allows you to get Gold, Eternium, Research Currency (used in Guild Research) Barrels (used in the Barrel Shop) and even Eternal Keys! Voyages are available in the Harbor.

The ship you send on a voyage is autonomous – that means that your hero is not blocked in any way while there’s a voyage active! However, there can be only one active voyage at a time.
Once completed, rewards for the Voyage need to be claimed!

There are 5 voyages on the list. Each takes a different time to complete.
The list is reloaded every few hours. When list reloads all unfinished or not claimed voyages are lost. The only exception is the last remaining voyage on the list – it can be claimed even after the reload.

Finishing all voyages on the list is rewarded with additional items.
Once you finished all voyages on the list, you can reload it by paying Gems.
When running short on time you can immediately end a voyage by paying Gems (the cost depends on time at which you want to skip) or watching an Ad to skip 30 minutes of active voyage.