Dungeons and Dragons has many different planes and places to explore, but one of my personal favorite is the Feywild. D&D Beyond has a terrific article on the Feywild and this is a good starting point, I think.
If the Shadowfell is bleak and dreary and full of inertia, the Feywild is basically the opposite. It is teeming with life, passion and change. So much so, that it can be genuinely dangerous or downright maddening to players not native to that plane. Even time behaves inconsistently in the Feywild.
Further, fey creatures tend to divide along either “Seelie” or “Unseelie”. Seelie Fey tend to be loyal to some degree or another with Queen Titania of the Summer Court, while the Unseelie tend to be loyal to the Queen of Air. The Seelie Fey typically are “good” while the Unseelie are seen as “evil”, but from what I can tell, these lines can be somewhat blurred. Because fey such as the Eladrin, can be so passionate, this might lead them to do some terrible deed even if they are otherwise good-aligned. Similarly, a dark Fey power may be swayed into helping a party for some reason.
Anyhow, a while back, my daughter’s campaign took an unexpected detour into the Feywild. What started as a minor side-quest turned into a major adventure in its own right after her party stumbled into a portal into the Feywild, and after exploring a bit came to the court of a powerful Unseelie Fey who put them through a lengthy trial. Eventually, they made their way to a large town mostly populated by satyrs who loved to revel so much that their town frequently burned down. They also came across a haunted cornfield and an old murder that was loosely based on this excellent adventure from D&D Beyond.
With the constant upheaval, exotic places, unexpected attacks from various Fey creatures in the forest and dealing with the time-displacement, the party was all too happy to finally get back into the Prime Material Plane several episodes later.
Looking back, the biggest challenge I found was coming up with enough Fey creatures. Luckily I had old copies of Dragon Magazine and old Monster Manuals to help fill in gaps for creatures that are fey and should be in there (but for which have not been ported into 5th edition D&D). Of course, as with any D&D adventure, you can also just make your own based on existing stats.
But if I had to do it all over, I would definitely make an adventure in the Feywild again. While there isn’t a lot of material on the Feywild (the Dungeon Master’s Guide and Mordenkainen’s Tome of Foes seem to be the best resources), the general principles of the Feywild were enough to make a solid adventure and really spark the imagination in the players.
Good luck and happy adventuring! 🙂