Are there any lower-level means of travelling between planes of existence?

Question

In Dungeons & Dragons 5th Edition, plane shift is a high-level spell that allows a party to journey between planes of existence. Are there any means available for lower level characters to journey between planes?

Plane shift is really convenient, with a casting time of 1 action and no expended material components – but as a 7th level spell, it is available only at 13th level, minimum. This means that only high-level parties can travel to the Feywild or the Elemental Planes.

Are there any spells (or similar abilities), that would allow lower-level parties to travel to other planes? Official material or third-party material is fine, as are setting-specific concepts/items.

Answer 1

Playing with planeswalkers

Since you are interested in setting specific features, the simplest way I know of would be to have the party play a group of planeswalkers, using the free Plane Shift Amonkhet supplement (from the Magic the Gathering setting).

It contains an appendix at the end called "Planeswalkers and the Multiverse" that simply allows everyone to travel between planes at any level, (although it is stated that this is recommended for higher level campaigns). This process is then an ability that all players simply have and takes about a minute of focus for a character to travel between planes.

Combining Blink and Banishment

Blink and Banishment, 3rd and 4th level spells respectively, can be combined to allow one to travel to the ethereal plane. Details on how to achieve this can be found in this Q/A.

Since Blink is self only this does require some extra work to do on a whole party (using Glyphs of Warding or Rings of Spell Storing would help), and this is still limited to traveling to the ethereal plane.

Planar Portals

The DMG has a section on Planar Travel which includes Planar Portals as a means of getting to other planes:

Passing through a planar portal can be the simplest way to travel from the Material Plane to a desired location on another plane. Most of the time, though, a portal presents an adventure in itself.

The section contains several more guidelines on what these portals look like, guardians for the portal, etc. In particular, PJRZ suggests hunting out details on the old Planescape setting (Sigil: The City of Doors in particular is all about this!)

This is naturally more of a story element that a DM can introduce rather than something that the players simply decide to do using their own abilities so is also a way for a DM to allow planar travel without giving the players too much power at lower levels.

Answer 2

Find a scroll of plane shift

Plane shift is still a viable option for planar traveling at lower levels, as long as you can find spell scrolls of it (or a high level wizard NPC that scribe such scrolls). The scroll can be used by low level clerics, druids, sorcerers, warlocks and wizards, as the spell scroll description says (Dungeon Master's Guide, pg. 200):

If the spell is on your class’s spell list but of a higher level than you can normally cast, you must make an ability check using your spellcasting ability to determine whether you cast it successfully. The DC equals 10 + the spell’s level. On a failed check, the spell disappears from the scroll with no other effect.

The DC 17 is kind high, but you can combine effects like guidance, enhance ability, and Bardic Inspiration to make your life easier.

Find a Horizon Walker Ranger

At 3rd level, the Horizon Walker ranger archetype gains the following feature (Xanathar's Guide to Everything, pg. 42):

Detect Portal

At 3rd level, you gain the ability to magically sense the presence of a planar portal. As an action, you detect the distance and direction to the closest planar portal within 1 mile of you.

Once you use this feature, you can't use it again until you finish a short or long rest.

See the "Planar Travel" section in chapter 2 of the Dungeon Master's Guide for examples of planar portals.

This feature is the best option you have to locate a "natural" planar portal.

Other options

If you want to travel to a specific plane, blink and banishment can be combined to travel to the Ethereal Plane, as explained here. If you want to travel to the Astral Plane, you can throw a bag of holding or similar item into the extradimensional space of a portable hole or Heward's handy haversack, but both items are destroyed in the process.