Dragon's Jaw

The Dragon's Jaw, also called the Strait of Throm or the Gate of Throm, is the narrow waterway between eastern Rhydain and Taijuria's western tip that joins the Sea of Surna (and, through it, the rest of the Sarpic Seas) to the Emerald Ocean by way of the Shreenwater. As a chokepoint for maritime trade, it has great commercial and strategic value; over the centuries, many empires and rulers have fought for mastery of the straits and of Thrommelport, the city that commands them.
The western shore of the Dragon's Jaw is formed by a sheer-sided mountainous promontory on the coast of Tythium called Dun Garna or Throm's Rock, with precipitous cliffs dropping down to the sea. The eastern side of the strait is formed by Cape Kueron at the tip of Peiramia, the west-reaching arm of Taijuria. Thrommelport stands here, on the steep slopes of the Cape's headland, facing Dun Garna across the strait and looking out over the gem-blue Shreenwater to the south. 
Although the straits are roughly six miles across at their narrowest point, much of their width is strewn with treacherous shoals, reefs, and jagged rocky islets that barely break the surface (or may be hidden just under it depending on the tide), with dangerous and unpredictable currents around and over them. The only safely navigable passage through the strait runs along its eastern edge, narrowing to within less than a mile of Cape Kueron's tip. Here a deeper channel with a predictable current allows ships to avoid the dangers of the rest of the strait; the fact that they must sail practically under the walls of Thrommelport to do so is what makes the city's location so crucial and allows it to control trade through the Dragon's Jaw so effectively.
The Dragon's Jaw is so-named not just for its angular shape and the dangers of navigation among its jagged (some would say tooth-like) rocks, but also for the winged sea-drakes that roost on the cliffs of Dun Garna across the water from Thrommelport. Legend tells that in olden days, some of these grew to great size and posed a serious danger to mariners in the strait, although the creatures that live there now are too small to threaten shipping and mostly prey on fish and gulls. However, some of the larger specimens could prove dangerous to a lone person, especially unwary or unarmed, venturing near their nests on the bluffs. They do occasionally take a lamb or young goat when careless Tythian shepherds graze their flocks too close to the top of the cliffs.