Not a lot. I've been to Viridian City, Pewter City, Cerulean City, and Vermillion City... The guards at Saffron City wouldn't let me through, and I only just got my Thunder Badge. I was going to try and find a way around to Celadon City afterwards...

[According to her town map, that really isn't a lot of Kanto at all.]

What's Mt. Silver like?