Up past the top of the citadel at the cradle. You go close to the far right side of the platform you fight on, then use the super jump to go up. There’s a long path up to the surface there, it goes to Nameless Town which just has a new type of passive bug you can afford to the bestiary and a memento. Tough but I dont think as tough as hollow knight? I haven’t played that since it came out so big grain of salt.