Go to Sector Space and you will have the option to beam down to Ketha Lowlands. Extremely annoying and makes no sense whatsoever, but that is how it currently works.
You can also get it from the city, you have to go to the gates near the Targ pits / crafting foundry. There should be two guards standing in front of a very large gate. At least this is where I always go to get there.
Same thing happened to me last week. The instructions tell you to see your contact in the Lowlands, but I just sat at the gates and couldn't get through. It turns out you just Hail your contact instead.
I'm glad I wasn't the only person confused by this!