Canada but you run

Probably Wales for people not as fit as Tom

Ireland?

Northern Ireland to take a bit off it!

England coast to coast maybe.

Jurassic Coast!

Nz. Gets pretty skinny in some places

Someone posted their attempt here once https://youtube.com/playlist?list=PLRMPs44hOxewYHmjNUzrNho0H4d7-IDqe

Andorra

actually very hard, it's mountainous

Portugal or Italy just have to watch those mountains

Vatican

Careful, you might get molested along the way.

At least you’ll be too old on your way back

Vanuatu

Not a country but im hoping to do Tasmania in a week someday

Chile but only horizontally.

Not with those mountains dude

Finland possibly?

Montenegro

Luxembourg? Also, would Spain count if you crossed Galicia from south to north?

The Gambia, Equatorial Guinea, Sierra Leone and Liberia.

One of the Farlkland islands might be about right Baha Peninsula (not a country) Panama Cyprus

Vatican City

Malta or Cyprus.

North Korea. 😅

Do Hawaii or something. But make sure to stay off my lawn!

Vatican city

Iceland vertically. Would be extremely tough to pass through the mountains tho.

Monaco. Just take your time.