This Legacy Chest is perhaps the easiest to access. It is located in the starting town of Cierzo, more specifically within the Cierzo Storage beneath the lighthouse.
All you need to access this chest is the Cierzo Town Key. This can be acquired from Rissa Aberdeen immediately upon joining The Blue Chamber Collective faction. Alternatively, you can acquire it from the town guard Captain, Burac, after completing the quest Vendavel.
Once you have the key, simply enter the Cierzo Storage and use it to open the large wooden door, revealing the Legacy Chest within.