Some of the Side Adventures in Tears of the Kingdom are tied to various side quests that need solving before they can be marked as complete. One example is the "Lucky Clover Gazette," which nets Link the useful Froggy Set armor. The Side Adventure "Investigating the Typhlo Ruins" rewards a unique melee weapon, but first, players will need to solve each of the ruins' four riddles.
"The Long Dragon" may be one of the later riddles for players to complete due to its prerequisites. Tears of the Kingdom has four temples that unlock the power of the Sages. For "The Long Dragon," players will need the Sage of Lightning.
Where is Typhlo Ruins?
If players are activating all the Skyview Towers, they can find the Typhlo Ruins Skyview Tower in the middle of the ruins themselves at 0343, 3133, 0180. These are to the very north of Hyrule between the Eldin Mountains and the Tabantha Tundra. They're also north of the Great Forest of Hyrule, but players can't leave the forest without taking a specific route, so they'll have to go around.
"The Long Dragon" Walkthrough
Near the Typhlo Ruins Skyview Tower is a campsite with a Zonai Researcher named Kazul. Activate the Skyview Tower to clear up the map of the Typhlo Ruins, then speak to him. Offer to help to get the "Investigating the Typhlo Ruins" Side Adventure. Then, approach each of the stone monuments to unlock four different side quests that make up the Side Adventure.
The slab to the far right is "The Long Dragon." Here's the riddle:
Display the power of the Sage of Lightning at the end of the long dragon that protects the mountain of death.
Before players can start solving the mystery, they'll want Vow of Riju. This is earned by completing the main quest "Riju of the Gerudo." They'll also need a bow and arrows.
The riddle mentions the "mountain of death" which is obviously Death Mountain in the Eldin Region. So, players are going to search along the eastern side of the Typhlo Ruins. The riddle also says to "display the power [...] At the end of the long dragon." Here's what to do:
At coordinates 0452, 3084, 0175 is a square platform made of stone. If players look straight ahead, they can see Death Mountain. Nearby the platform is the ruins of a snake-like body buried in the ground. There's no need to follow it, but doing so will lead players to the statue of the dragon's head.
- Standing on the platform at 0452, 3084, 0175, use the Vow of Riju.
- Wait until the yellow field envelops the "tail" of the dragon.
- Draw the equipped bow with ZR-button, and fire it at the tail/ruin protruding from the ground.
If done correctly, the platform that Link is standing on will rise out of the ground to reveal a treasure chest. Jump down and loot it to gain x3 
Topaz. "The Long Dragon" side quest will then be marked as Complete in the Adventure Log.
The Legend of Zelda: Tears of the Kingdom is available for Nintendo Switch.