Where is the piano puzzle in Undertale?

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Tags

1. #intersection
2. #waterfall
3. #played
4. #three
5. #total
6. #eight
7. #directional
8. #arrows
9. #different
10. #where
11. #located
12. #playable
13. #first
14. #shyren
15. #saying
16. #found
17. #notes
18. #plaque
19. #puzzle
20. #piano
21. #north
22. #contains