10km (6.3 miles) eggs hatch into rare Pokemon, such as Chansey and Aerodactyl. Here is the rarity chart of Pokemon hatching from 10km eggs.
Do 10km eggs hatch into Pidgey? | PokemonGo
6 things you should know about eggs | PokemonGo
Tips for Hatching Eggs in Pokemon Go | PokemonGo
The rarity of Pokemon hatch from 2km eggs | PokemonGo
The rarity of Pokemon hatch from 5km eggs | PokemonGo
How to discard 2km eggs | PokemonGo
What is DPS and EPS in Pokemon Go?
[Video] Zapdos defeats Elctabuzz and Vaporeon
The best 4 Pokemon to defeat Moltres
Oddish