I recently purchased the adventure Fane of the Fallen because it's an adventure for characters level 13 and up, and high-level modules can be hard to find. It's also by Frog God Games, and I tend to find their work pretty reliable.
I purchased a hard copy because I really do prefer physical media for running games, especially given how dense this particular publisher makes their content. There's not much white space in Frog God's default layout, which I find difficult to parse. Because PDFs rarely fit nicely onto the widescreen of my laptops, I find it much easier to use a physical book. I assume the dense layout is an effort in cutting costs, and I guess it's good that they do it, because this adventure was US$33. Is it worth it? In short: yes. Read on.
There are some minor spoilers here, so if you're a player, then you may want to skip the story section. Then again, I'm not revealing anything that's not on the back of the book, either, so this is only a nominal warning.
Fane of the Fallen tells the [back] story of a group of elves who chose to follow the succubus Lilith, elevating her to a goddess. As a result, they become "fallen" elves, with a ruler (Novgorod) dedicated to the succubus goddess. In recent years, humans have begun to encroach upon Harwood forest, the home of the fallen elves, so Novgorod has cooked up a scheme to steal a magical book so it can be used in a ritual to summon Medb, a warrior of Lilith.
That's pretty much where the 137-page adventure starts: orcs attack a town and raid the library in search of the magical tome. The players have to unravel quite a lot to connect this seemingly random and uncharacteristic event to the ultimate plot, and following the trail of this inciting incident is about a third of the adventure.
Some small maps are provided as reference in the text, but it's up to the DM to translate those to a table matte. The maps are not available as a high-quality PDF, either (the PDF version has maps, but they're small and they are not infinitely scalable). I've never loved the quality of Frog God maps anyway, so the absence of them is not deal-breaker for this module by any means. It just means the DM has to do a little extra sketching, but none of the maps are very complicated and very few require great precision, so it's something you could easily do at the table, as needed.
There's also a considerable side quest they must undertake in order to advance the story, and it's a good one. In fact, it's an extra-planar side quest, which you can play up as much as you please. I'm a longtime fan of Planescape, and I'm always looking for an elegant way to introduce players to that setting, so I consider any mention of planeswalking a perfect gateway (so to speak) into Sigil or the Infinite Staircase.
This particular adventure opens with a book robbery. In Planescape lore, the Infinite Staircase is a fixture in a trans-dimensional library, intersecting lots of different planes at various plateaus. It's a perfect connection to incorporate when the side quest. The local library can easily turn out to be a portal to the base of the Infinite Staircase, which in turn provides access to other planes for the players. It's easy, it's thematic, it feels natural, and it gets your players familiar with what may be a new setting for them.
The plane as written in the module is not one you'll find in Planescape, but there are easy analogies, so it's easy to adapt. Or you can just insert a new plane and ignore that one particularly studious player who returns to the game next week with a map of the cosmos and several questions about the exact location of this unlisted plane.
Of course, if you have no interest in Planescape or in emphasizing the multiverse of D&D, then the module natively provides a serviceable path to the other plane. The quest-giver is a magic user and happens to have a portal for the players to use. Clean and simple.
The adventure is a great mix of open exploration and dungeon-style encounters. This is a pretty familiar formula, but that's because it serves D&D really well. It keeps the players focused, it ensures that the game progresses in the direction it needs to go, and it optimizes the experience for what D&D was designed for in the first place. In fact, pages 138 to 167 consists of wandering monsters, magic items, and new creatures (well, new if you don't already own Tome of Horrors), so your players are sure to get that sense of discovery as they fight their way through forests and towers and planes.
People say that high level adventures are hard to find. And they are, at least compared to entry-level adventures, which are so common that I think it's safe to say that most adventures published by Paizo or Wizards of the Coast start at level 1. You get more variety in third-party publishers, or if you're happy to jump into book 3 or 4 of an ongoing adventure (and hope that the story can make sense after a quick "our story so far..." info dump at the beginning).
You might initially wonder why it matters whether something's written for a low level or high level. After all, the system is well-designed and well-documented, so a DM really only has to apply some level-up templates to the monsters, or drop in high level approximations, and a level 1 adventure can become a level 10 adventure. That is strictly true, but in the very first encounter in Fane of the Fallen, there's a paragraph that sums up perfectly the difference between an adventure adapted for high levels and an adventure written for high levels.
The demonstrative paragraph tells the DM how to handle the initial fight with some orcs. It's pretty straight stuff until it mentions that some players may capture the orcs and question them. And in the next encounter, there's a similar paragraph allowing for the possibility that some players may attempt to charm their foes, and what the DM should do in that case.
This is simple, by-the-book detail, but it's detail that only makes sense for a high level party. Imagine a bunch of 1st level characters having the wherewith all to capture a group of orc raiders, much less having access to a charm spell to use on the brute squad. The DM of a low-level adventure doesn't have to think about that sort of thing. Even if the players are clever enough to try that, there's no reason to believe that the character would be capable of disarming and capturing their foe, should the DM feel uncertain of what kind of information a captured enemy would and would not know.
It's little touches like these that make high-level adventures unique. It's details that low-level adventures don't need to consider, bigger and better foes, grander schemes, cooler spells, extra-planar excursions. This module demonstrates this difference nicely, and it happens to be well-written in general. If you're looking for an entertaining plot, a nicely paced adventure that encourages you to move through the story at a reasonable pace, and a nice challenge, then you ought to consider this module.