Quick answer: The Broken Puppet Valley bell is on the Weeping Creek Valley floor by a stilted house, reached from Red Thread Barrier via a chain swing, ladder and drops.
Red threads block the straight line between the two bells, so you have to take a longer route along the cliffs. Expect fights along the way, including one right at the bell.
Where the Broken Puppet Valley bell is
The bell sits on the valley floor in Weeping Creek Valley, close to a house raised on wooden stilts, with red threads strung across the area. When you rest there, a menu titled “Broken Puppet Valley” opens with Traverse, Upgrade Equipment, Store, Train Abilities, Save and Leave.
It comes right after the Red Thread Barrier bell, but a curtain of red threads next to that bell cuts off the direct path. The walking route loops around it with a swing on a hanging chain, a cliff path, a ladder and two short drops to the valley floor, and you will fight along the way.
You know it worked when more of the Weeping Creek Valley map fills in after you ring the bell, and Map Completion rises to 11%.
How to reach it from the Red Thread Barrier bell
Start at the Red Thread Barrier bell (every bell is in the full list of bells). Red threads beside it prevent you from going straight ahead, so move onto the rock ledge at bell height and stop about 13 m from a chain suspended in the gorge.
Look toward the chain and raise the camera angle. Adjust it until a small circle displaying a Space prompt appears on the chain.
Press Space. Soul grabs the chain and swings over the gorge, reaching the opposite side.
Follow the ledge uphill to a plank walkway attached to the cliff. Red threads hang above the planks at the far end, where railings enclose a dead end.
Turn around and take the upper path in the opposite direction. Before you reach the ladder, two sword-wielding brutes drop down onto the path and attack, so be ready for a fight.
Reach the plank platform at the ladder’s top, then press Space to descend. Make two short drops from there to reach the valley floor.
Follow the valley floor to the bell. A camp of spear and sword enemies, plus a woman with a long blade, waits on the floor near it, so clear the fight first and then press E at the bell.
