This is just a quick achievement guide. Most of the achievements in the game are pretty simple, but finding the secret ones can be difficult, so I thought I'd help out.

These are the ones that aren't secret and tell you how to get them.

Allies in Dark Times: Use an ally or have one in play.

And I Would Walk 500 More: Travel 500 miles by road.

Darkness Reigns: Win as Dracula.

Empty the Chambers: Use Holy Bullets 15 times across all your games.

Enough talk... Have at you!: All four Hunters fight Dracula together.

Hunter... or the Hunted?: Play online.

Once Again Given Flesh: As Dracula, heal at Castle Dracula.

Peace Returns: Win as the Hunters.

Tooled Up: Complete all core game tutorials.

"We Meet Again, Foul Creature!": As a Hunter, fight Dracula.

These are the hidden achievements, probably the reason you clicked this guide. They are in alphabetical order, with the name and how to unlock.

A Most Unholy Act: As Dracula, place the Desecrated Soil encounter card.

A Sea of Wonders: Embark onto the sea from a port city.

Another One Bites the Dust: Bite 50 Hunters across any number of games.
(Thank you to Marlex in the comments!)

Dracula Done Quick: Win as Dracula in the first week.

Dracula's Delight: Use the supply action at night.

Live to Bite Another Day: As Dracula, escape combat using Escape as Bats.

My Psychic Sense is Tingling: As Mina, use your special ability and discover that Dracula is in your region.

"My Unholy Army is Complete!": Mature 25 vampires across all games.

No Need to be So Salty!: As the Hunters, cause Dracula to die at sea.

Oh the Places You'll Go!: Use a train.

Out of Options: As the Hunters, Dracula has no legal move options. (This can be tough to pull off, but basically he has to be blocked in by his own Trail and you can help with Consecrated Ground and Heavenly Host tokens.)

Shadow Walker: As Dracula, have a full trail with no discovered locations.

Sharing is Caring: Trade an item with another Hunter.

The Quickest Hunters in Europe: Kill Dracula in the first week.

To Lose in Toulouse!: Kill Dracula in Toulouse.

Special thanks to Lord David the Terrible at the Nomad Games Discord for the unlock conditions for No Need to be Salty and Out of Options, and help brainstorming for Another One Bites the Dust and Unholy Army is Complete. Thank you to ****luca in the comments here for the help with "My Unholy Army is Complete"! And thank you to Marlex for finishing it off with the unlock condition Another One Bites the Dust! We're done, enjoy!