Every time I try to enter Riften, I'm told to use the North Gate. Where is this North Gate, I can't find it for the life of me. The was a guard at the docks I tried to persuade to let me in, but that failed and now there's no dialogue options with him. I'm finding this really infuriating, doubly so because it's such a dumb thing to be stuck on. Please help!

When i ran to Riften some guard tried to charge me for entry - i used the Intimidate option ('This is a shakedown!') and he let me in for free

Just walk around the edge of the city until you get to the north gate.