Collectible can be found inside Newt Cave dungeon. This is the hardest dungeon to solo. What makes it hard are Trolls in the area. These trolls are not regular difficulty level enemies. They are extremely hard to defeat.
Avoid the troll at the dungeon and enter the cave. You can do this by pulling him from the nearby main road. Start running north. You can spot a small hill close by. This is the area above the cave entrance. Jump to it, and enter the cave before the troll is back. There are couple of trolls at the start of the dungeon as well. You can skip them and/or pull toward the southern cave room. They stop to follow you there. Now you can proceed toward the last room. Shard is inside this part of the cave, but there are more trolls… If you are extremely careful you can skip them as well. Stealth gives you a huge advantage here.
Newt Cave approach.
The Dungeon entrance map location.
Zoomed out map view of the entrance.