Threshold

When I wrote the D&D Classic series in the 1980s (aka BECMI), I needed to specify a 'starting point' for a campaign.  Thus was born the town of 'Threshold', created out of whole cloth to serve that purpose.  Others have developed it into a wonderful place, rich and vibrant.  (I had nothing to do with that development, hat tip to others.)

Frank Mentzer, Facebook (Feb 12, 2020)

Threshold; 1 hex = 500 feet (revised to 1 inch = 500 feet in GAZ 1), from the D&D Expert Rulebook (1983)

Mentzer explained the rationale behind his choice for a name in this post on Dragonsfoot in July, 2008, (defined as "any place or point of entering or beginning")*

*also used as the name for the Mystara fanzine

From the Expert rulebook (pg. 38):

This, the Home Town of most PCs, is a thriving frontier village of 400 permanent residents plus over 100 other regular visitors.  The main business of Threshold is to supply timber to the Capital.

Commerce (pg. 38-9): 

The following items are shipped by boat from Threshold to Specularum: Armor (leather and shields only); Craft products (pottery, baskets, wooden items, etc.); Food (grains, fruits, etc.); Furs; Herbs, including wolfsbane; Honey and Wax; Ice from the mountains; Magic items and Monster parts found by adventurers; Ores (a small local business); and crude weapons.

The following items are shipped by boat from Specularum to Threshold: Trained animals (including all warhorses); Armor and weapons; Exotic cloths (silk, velvet, etc.): from city trade; Exotic trinkets (imported from other countries); Foods (such as seafish); Glassware; Medicines; various Metal goods (lock mechanisms, pots & pans, spoons, hardware, etc.); Metals not found locally (tin, copper, etc.); News; Oil (whale, olive, and others); Parchments and inks; Potions (though rarely); Salt (bagged or in blocks); Spices; Steel Tools; Wine and Ale; and visitors, traveling entertainers, and occasional government officials. 

Travel from Threshold (pg. 39):

One trail follows the river, leading southeast to Kelven.  The trade route between Specularum and Selenica passes through Kelven; the well-worn riverside trail leads south (through Krakatos) and north (to the small mountain outpost of Highdell, at the river’s beginnings). 

A rarely followed trail leads east from town, winding into the hills (leading to the gnomish mines). No trails lead north or west.

Map of the Grand Duchy of Karameikos, from the D&D Expert Rulebook (1983).  The villages of Threshold and Kelven were added, as well as several trails/trade routes not appearing in the earlier version of the D&D Expert Rulebook (1981) 

The BECMI version of Karameikos could potentially coexist within the B/X version, since villages were not indicated on the map in the 1981 rulebook, (Luln was designated as a town, whereas Threshold and Kelven are both indicated as villages).*

*notwithstanding the similar populations of Luln and Threshold (both 500)

However, a human frontier town so deep in the wilderness has major implications for the setting.  The BECMI version of the Grand Duchy could alternately represent Karameikos a generation later, with human civilization having made significant inroads.

Night's Dark Terror:

Illustration by Helen Bedford, from module B10 "Night's Dark Terror" (1986)

Module B10 "Night's Dark Terror" (1986) by Jim Bambra, Graeme Morris, and Phil Gallagher expanded upon the Sample Wilderness and Home Town section in the D&D Expert Rulebook (1983) to create a more fully realized vision of Karameikos and Threshold.

The map of Eastern Karameikos designates the trails/trade routes as either main roads (between Specularum and Selenica) or minor roads (from Threshold to Kelven) and also indicates the rarely followed trail into the hills east of town as a path.

The 6-page section on the town of Threshold presents a grittier feel, in comparison to the writeup in the D&D Expert Rulebook.  Information on the Clerical Court, the Town Guard, various Taverns/Inns, and Fogor Isle is included, as well as a table of optional events.