Between the main story, Shrines of Light, and side quests, there will be no shortage of things to do in Tears of the Kingdom. Those that stop by Tarrey Town will find several side quests including "Secrets Within."
It's not as narrative-heavy as another Tarrey Town side quest, but "Secrets Within" makes use of the Zonai Dispensers. Tears of the Kingdom players may already know how to use Zonai Dispensers if they used the one on the Great Sky Island in the tutorial mode. However, taking the time to demonstrate the dispensers' capabilities in the "Secrets Within" side quest may earn Link a modest reward.
How to Unlock "Secrets Within" Side Quest?
"Secrets Within" is obtained by speaking to a man named Pulcho at the Hudson Construction Site. This is to the west of Tarrey Town at coordinates 3800, 1564, 0091. Pulcho is standing right next to the Zonai Dispenser, so he's hard to miss.
Players can reach the Hudson Construction Site three different ways:
- By launching from the Ulri Mountain Skyview Tower (3493, 2019, 0188).
- If players have completed the "Rock for Sale" Shrine Quest, they can travel from the Jochi-ihiga Shrine instead.
- Finally, there's the Rasitakiwak Shrine, which is on a hill overlooking Tarrey Town at 4166, 1323, 0229.
"Secrets Within" Walkthrough
Speak to Pulcho to add the "Secrets Within" side quest to the Adventure Log. All TotK players need to do to complete the quest is walk up to the Zonai Dispenser and drop in a Zonai Charge. This will cause capsules of Zonai Devices to spill out of the machine.
- Open the inventory with (+) and tab over to the Materials page.
- Select a Zonai Charge (optional: select up to five) and exit out of the menu.
- Press A-button near the dispenser to drop them in.
Most Zonai Dispensers can be found on the Sky Islands, but there are a few located on The Surface and even in The Depths. Each Zonai Dispenser generates different Zonai Devices. Players must use the Zonai Dispenser and get one of each Device in order to register the dispenser's list on their map.
Large Zonai Charges generate more Zonai Devices than regular Zonai Charges. One 
Large Zonai Charge is equal to five Zonai Charges.
Here is every Zonai Device from the Hudson Construction Site's dispenser:
Fan
Small Wheel
Balloon
Big Wheel
Rocket
Steering Stick
Where to Find Zonai Charges
If for some reason players do not have any Zonai Charges, they can collect them from Zonai Constructs. These enemies are found on The Surface but only near ruins, or on the Sky Islands. They are also the primary enemies at the four Temples. Defeating one will earn players one regular-sized Zonai Charge.
Players can also pick up a Zonai Charges by inspecting inactive Zonai Constructs. Large Zonai Charges are sometimes treasure chest-rewards in the "Rauru's Blessing" Shrines.
If players have some 
Zonaite to trade, they can go to any of the Zonai Mines in The Depths or on the Great Sky Island and trade them with the Steward Construct near the forge. Players can even get Large Zonai Charges here. Since this involves trading Zonaite, which can be traded for Crystallized Charges (which are used for increasing the Zonai 
Battery), it's not a recommended way of farming Zonai Charges.
"Secrets Within" Side Quest Reward
As a thank you, Pulcho will give Link a 
Sundelion. He'll then tell Link about the Zonai Dispensers in Kakariko Village and the one by Digdogg Bridge. Also, Pulcho won't collect the Zonai Devices from the machine, so make sure to grab them all before leaving.
Sundelions can be cooked into meals for curing gloom. Cooking five of them together can restore up to 15 hearts that have been lost to the gloom effects. They're also a requirement for completing the following side quests:
- Mattison's Independence (x10 Sundelions)
- Gloom-Borne Illness (x1 Sundelion)
The Legend of Zelda: Tears of the Kingdom is available for Nintendo Switch.