Gladius Legis
Legend
The climb doesn't specifically not call for an ability check, either. Whether or not it requires a check to climb a free-standing rope is one of those things that's left up to DM interpretation. There's certainly nothing in the spell description to indicate that this rope is easier to climb than other ropes.
The Athletics entry (p. 175 PHB) makes it quite clear what climbs call for an ability check. It does not include a free-standing rope.