Meet Treebot, a robot that can climb irregularly shaped trees autonomously.
The design of Treebot is fairly unique: it uses a set of flexible linear actuators connecting two gripping claws to allow it to move around like an inchworm. While the back gripper holds on, the front gripper releases and the body extends forward, allowing the robot to literally feel around for a good place to grip.
When a more advanced version is developed, one that has greater maneuverability, adaptability and durability (plus the ability to harness the metabolic energy of trees), drop thousands of them to the Amazon, each one with the instructions to recreate Notre-Dame out of the rainforest.
Once deployed, they'll link up together to form a chain: one treebot gripping another. This chain will in turn knit itself with other chains to create a lattice binding trunks, branches, vines and canopies together. It is also anchored to the forest floor. Simultaneously, the treebots will attach themselves to these future columns and buttresses like a full-body orthopedic brace of facehuggers.
This mesh system will slowly reconfigure itself, contracting segments here and elongating segments there, along the way guiding and controlling the growth of the trees. Once it begins to look like a 3D grid model of the cathedral's superstructure, or a scaffolding without the building, the autonomous swarm will then coppice and pleach and pollard and espalier and inosculate a dense thicket to fill in the grid and fully enclose bosquets of chapels, atriums and honeycombed crypts.
In but one narrative thread we can choose to trace through the ensuing decades and possible centuries of micro-silviculture, we see this project gradually getting purged from the collective memory, Onkalo-style. Long before the work is completed, it's completely forgotten. But the work continues apace until it's finished, when, per their programing, ancient by now, the treebots go into hibernation, frozen like gargoyles. They wake only when some trimming is needed.
For a long time, the finished facsimile remains lost the descendants of its original programmers, to the whole of humanity in fact. There's no one to explore its understory caverns, no one to listen to the nesting critters singing their cacophonous hymns in a neverending liturgy. There's no one even to climb it.
Then one day, just by accident, members of an uncontacted tribe stumbles upon it. In need of a new settlement, they move in and make it their new village: a vegetal Notre-Dame transformed into a longhouse. Amazed and bewildered as well by the still scampering treebots, the tribe develops a cargo cult around them, venerating them by placing fruits, animals and the occasional virgin on the leafy altar.
Quite mysteriously, the tribe leaves, never to return. Notre-Dame is abandoned. With the treebots no longer functioning, it becomes a ruin, its giant columns toppled over and overgrown with itself. There are no more master craftsmen to tend to the garden, nothing to dam the natural, unhinged forest from flooding back in. Everything rots away.