During your journey in the Treasure Cave, you'll surely come across a strange magic circle of blue light. What's that, you ask? That's a Portal!
Unfortunately, it's not active yet. To enable it and continue your journey to the depth of the Treasure Cave, you need to gain a Portal Stone. It is a unique and rare item to gain, but the Delivery Festival provides you with this opportunity!
Complete Deliveries, open Delivery Chests and you'll have the chance to receive the Portal Stone!
After you activate the Portal, it'll be activated and you'll be able to use it to explore even the Treasure Cave further.