For this challenge, you must grapple 3 hanging quipus, just like the ones you used to cross the canyon when you first arrived in the city. The quipu locations are marked with orange dots on the annotated level map and shown in these screenshots.
One of the quipus is hanging just northwest of the Fluent Yucatec monolith (#5 on the map), where the orator in the gold mask is getting the crowd all riled up.
Climb onto the wooden platform nearby in order to grapple the quipu.
Another quipu is hanging above the Proficient Yucatec monolith in the southern part of the city. (It's monolith #1 on the map.) Start here, on the ledge above and to the west, near the second outcast from the Dice with the Dead Mission. Jump out and grapple the quipu to initiate the challenge.
A third quipu can be found in the ABANDONED VILLAGE, where you first met Etzli and Unuratu. It is covered a bit later in the walkthrough, but if you want to, you can go there any time by following this path through the jungle to the northwest.
When you get there, you'll discover the Abandoned Village Base Camp, making travel back and forth easier in the future.
Turn around and climb the curving stairs near the campfire.
The quipu is hanging just beyond this ledge. Jump and grapple it to complete the challenge. Depending on where you are in the game when you discover it, you can finish exploring the ABANDONED VILLAGE, return along the path to the city, or use the base camp to fast travel out.