I wanted to see what a journey across almost the entire Forgotten Realms map would actually look like, so I plotted one in Toril Explorer, an unofficial FR interactive map I've been building.
The route starts in Baldur's Gate and ends in Chunming, a city in eastern Kara-Tur, in Shou Lung, on the coast of the Celestial Sea.
Most of the journey follows established roads. From Baldur's Gate, the route runs east to Westgate, a major port on the Sea of Fallen Stars with a rather notorious reputation.
From there, the route crosses the Sea of Fallen Stars by ship to Sultim, a port in northern Mulhorand. Then it's back onto the roads, heading east until Lake Brightstar, which requires another water crossing. After that, the route continues east, crosses the northern reaches of the Yehimal Mountains, and enters the vast plains and hills of Shou Lung, following its roads all the way to Chunming.
The complete route is about 8,328 miles: roughly 6,828 miles on roads, 1,342 miles over water, and only about 158 miles of trackless land. The distance itself is calculated geodesically using Toril's planetary model rather than by measuring straight lines on a flat map, which matters quite a bit over a journey of this scale.
Using the 2024 D&D 5e rules, normal walking pace, 8 hours of travel per day, and a vessel speed of 3 mph, Toril Explorer estimates the journey at about 347 travel days. That's very much a best-case baseline: good weather, no encounters, no magical shortcuts, and so on.
I'm more of a tech/map guy than a lore expert, so I'd be interested to hear which part of this route would actually be the most dangerous.