This room has a piano next to the wall. you are able to play by using arrow keys and Z. X to stop playing. the sign tells you that you hear a tune throughout the halls. if you ran into the shyren encounter before entering, it isn't that. there is a door in the middle of the sign and piano.

now, you want to exit the room and keep going right. you'll soon get to a room with a statue that's being rained on. it looks sad.
keep moving on. remember the statue though.
soon enough you'll run into the umbrella bucket. take an umbrella. do NOT encounter monster kid and take him with you. if you do this you'll have to go through the undyne chase and help monster kid. then backtrack.
go back to the statue with an umbrella.
press Z on the statue
click yes
Listen to the music you will encounter later on if in a pacifist run. above the statue's head, the notes will appear in the order you play them.

if your too lazy to read my guide then here is the code
wow. did you really think I would let you do this? pfft. get rickrolled hard buddy.

the horns of this statue seem to look like the same horns prince Asriel has in your fight with him. the statue is looking down. presumably at the smaller rocks below. it also seems to be holding something. I believe that this is a statue of Asriel. Asriel is tending to some flowers in the statue. the flowers are also in the statue as well. after your battle with asriel, you see a bunch of pictures of asriel helping chara. while looking at them you hear His Theme. this is the same music played by the music box. coincidence? not in undertale. according to fandom, and fanfic (GlitchTale) Chara and Asriel put the music box into it themselves.

once you get to the room with the artifact, walk into the room and pick up the gem.
but wait...
why?
oh.
your inventory is now filled with a dog.
oh well.
just drop the dog.
it IS the annoying dog from papyrus' fight.
...
the dog took the artifact...
huh... guess I get nothing..
nah
if you check your inventory, it's filled to the brim with dog residue. sells for 4 gold(guide used to say 3 gold but LowestDesert89 said it was 4 and I trust him/her) at the most at temmie's shop. when used it fills your inventory with residue. some residues fill your inventory with dog salad. make sure to get dog salad before a fight. it's useful.

drop all of your residue but 1 residue. use the residue to fill your inventory with residue. keep doing this until your inventory fills with dog salad if you want salad. if you don't keep doing this and selling to temmie for cash. boring, time consuming, but worth.