You can only get this quest from ONE of the zones listed above (unlike before when you could have gotten multiple times).
You can enter The Caves from the Down Below. The zone-in point is in the heart of the zone. There are several twists and turns before you reach it. There are zone-outs on either side to South Qeynos and Qeynos Harbor.
Don't worry - once you are inside there are two travel bells to expedite movement outside this zone.