Maracaibo
What happens on the homeward bound spaces 20, 21a, 21b and 22?
The designer confirmed that these spaces are cities with only the scroll action, and the rulebook describes them the same way.
All four are cities and you must stop on them. Space 20 lets you choose a combat action or move your explorer up to 2. On 21a or 21b you score 3 VP and on 22 you score 5 VP, and nothing else. That scroll is the only city action available and you would never skip it. Free actions such as completing a career goal remain allowed, even after the main action on space 20.