Planes of Power
While the Horizon Walker is a Ranger which guard the world against external threats, the Planar Explorer is the sort of Ranger whose curiosity leads him to wander those plans. The Planar Explorer is a Ranger archetype. Hit Points, proficiencies, saves, and skills are unchanged from the PHB (page 89).
At 3rd level, you become proficient in the Planar Cosmology skill. Additionally, at higher levels, you can choose specific planes with your Natural Explorer class feature. The benefits of this feature cannot override specific effects tied to a plane (for example, you can still get lost in Pandemonium, and the elemental soup of Limbo can still slow your party’s speed), but it is possible for this feature to mitigate those effects to some extent.
At 3rd level, you can deal extra damage to your favored enemy. This damage is equal to the rage damage of a barbarian of your ranger level. When you go up a level and gain a new favored enemy, you can change this ability to target that favored enemy. You cannot use this ability on more than one type of favored enemy.
At 7th level, a Horizon Walker has become a bit of an expert and traveling through portals and breaches. When next to a portal, a Horizon Walker can spend a minute examining it to determine the plane to which it leads. A Planar Cosmology roll may be called for.
Improved Planar Enemy
At 11th level, you can apply the Planar Enemy damage to two types of enemies.
At 15th level, choose a home plane. You can Plane Shift, as per the spell except no components are needed, to this plane once per long rest. If you are ever subjected to a Banishment spell, you can choose to be banished to your Second Home instead of your plane of origin.