The Expedition Letters
One physical letter each month, written by Rufus Hightower to Anna Bell Darrow from wherever the expedition has reached.

Expedition Letters is a physical-mail subscription from inside the Rufus Hightower Universe. Each month, subscribers receive a new letter written by Rufus Hightower and addressed to Anna Bell Darrow while Rufus travels on dangerous expeditions with the brilliant, and frequently troublesome, Dr. Archibald Funk.
These are personal letters sent home from an adventure still in progress. Rufus writes to Anna Bell about the places they have reached, the people they have encountered, the trouble Dr. Funk has caused, and the growing evidence that certain locations may be connected by something known as the Convergence Points.
Alongside Rufus's correspondence, subscribers receive a changing assortment of companion materials connected to the story. These can include illustrated maps, tropical drink recipes, stickers, telegrams, photographs, expedition documents, and other surprises from the field.
Each delivery tells a satisfying chapter while gradually contributing to a larger seasonal mystery. A map included one month may become essential later. A drink recipe may originate from a location Rufus has just visited. A name mentioned casually in one letter may return several months later with an entirely different meaning.
The first season follows Rufus and Dr. Funk through Peru in 1937. Rufus believes he is documenting another expedition. Anna Bell may be the first person to realize that he is walking toward something no map was meant to contain.
What Arrives Each Month
A new chapter
Story inserts
Drink recipes
Clues worth keeping
Anna Bell is doing the filing
The letters are addressed to Anna Bell Darrow because someone has to be assembling them. She catalogs the correspondence, compares the maps and notices the repeating names, symbols and locations before the expedition crew works out that a pattern exists.
Rufus thinks he is protecting her by telling her only part of the truth. In practice she is usually the first person to understand what the truth means. The subscriber reads over her shoulder, which is why a map from one month can matter six months later.