Up to 5 ropes may be taken from Nyriki's crate for free. Ropes respawn on the ground at the Musa Point general store. An unlimited supply of rope can be found in the Brine Rat Cavern, near the skeleton Fremennik. After partial completion of Royal Trouble, a very quick, unlimited supply of rope can be found by searching a crate in the Miscellanian dungeon area, after squeezing into the lift room. If one has built a rope rack in one of the four possible locations, an unlimited supply of rope may also be obtained there.
Ned gives the illusion that he creates rope from wool. However, he actually trades it with Jofridr Mordstatter of Neitiznot in exchange for rope. After The Fremennik Isles, Ned will provide a 1-time second rope for free in exchange for silence.
Rope is used with terrain in at least three different ways:
Permanently placing the rope on the terrain. The rope simply remains there, allowing you to always pass the obstacle. The one used to enter the A Soul's Bane rift is one such example.
Placing the rope on the terrain and losing it after limited use. For example, a rope is required to enter the pit where the Genie resides west of Nardah. When you leave the pit (whether by climbing up the rope or by teleport), the rope disappears. This requires you to bring a new rope each time you visit.
Placing the rope on the terrain and getting it back after passing the obstacle. It automatically returns to inventory when you get past the obstacle. The rope used on the rock to enter the Mountain Camp is an example of this.