If you are talking about Mt. Coronet you have to know how to Surf. If you are talking about from Route 205 you need to go through the Eterna Forest.
you get it at the cave on the right of eterna city :D
She is in Eterna city gym. you must help Cheryl through Eterna forest to get to Eterna city. But first go home into that cave you could not get through before. Use Rock smash and get through the cave. Ask others for more help.
Below Eterna City's cycling road
The Cave near Eterna City Cycling Road
She is in Eterna city She is in Eterna city She is in Eterna city She is in Eterna city
use escape rope i got 44 in that place
you have to back yo jubilife city and head north into a cave and use rochsmash then just follow the route until you get to floraroma town from there you have to battle Mars, then you go through eterna forest and head into eterna city. (Spoiler, Cynthia will give you an egg that hatches into a togepi).
no its in eterna forest near the entrance to eterna city
go to the bicycle route at Eterna city and then once you reach the end there will be 2 paths choose the right one
u just go in the cave near celestic town and go left or near eterna city then go right
to the left of eterna city,
you cant go to eterna city in kanto only in sinnoh