The city gate in the wall at the far end of Edgeway Road. It is opposite the Hubwards Gate, but the whole axis is rotated clockwise so that neither faces its named direction. The mapp calls it the Rimward Gate, but the "s" comes and goes.
The revised and expanded city map contained in The Compleat Ankh-Morpork has a handy little panel illustrating how all roads lead to Ankh-Morpork, even if you happen to be leaving the city and walking in the opposite direction, In this case out of the Rimward(s) Gate, where the road leads to Ankh-Morpork via Sto Helit. Incidentally, The Compleat Ankh-Morpork uses Rimward Gate pretty consistently throughout.