A 50k lumber box is an item in Evony TKR (The King's Return).
The description of 50K Lumber Box in Evony TKR says:
Use it to gain 50,000 Lumber.
50K Lumber Box is known to potentially be obtainable from opening Senior Resources Chest, Senior Alliance Boss Package, Lucky Box Ⅰ, Junior Lava Turtle Chest, Junior Golem Chest, Junior Witch Chest, Junior Warlord Chest and Common Ymir Chest. The links for each item are below:
Note: This list may be incomplete.