Why Hello Miss Fade!
http://www.mizahar.com/lore/Distance_ChartI believe you may find your answer here. =)
It looks like Syliras -> Riverfall is 2125 miles in a straight trajectory. I may be mistaken but doesn't Endrykus move around? It may be hard to find. Syliras to Alvadas is 1375 miles, and the distance between them would put you a good ways into the Cyphrus region I'd say. So maybe somewhere between 1375-2125 miles... I don't know how fast your horse goes or anything, but i'd say a number comfortably in the middle of those two or so, divided by your speed.
I'm checkin' up on this as we speak and will edit this when I get the correct answer.
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Okay, essentially i've learned that you will need a Drykas guide if you want to find the city quickly rather than riding all over Cyphrus looking blindly. The Drykas can find it relatively quickly using webbing. I think the distances I mentioned still stand.