There is a full fast travel system in Gotham Knights, outside of just traveling to the Belfry. This guide on How To Unlock Fast Travel In Gotham Knights will tell you what you need to do in order to unlock the side case that you need to complete if you want to unlock full fast travel.
After you finish the first couple of nights worth of investigations you will be able to fast travel to the Belfry. This is actually quite useless as it’s only useful when you want to finish the night and move on. However, there is a more traditional fast travel system that you can unlock that will allow you to fast travel to each of the different districts in the city, this makes getting around the map so much faster, so it’s more than worth it.
How To Unlock Fast Travel In Gotham Knights
Unfortunately, you do have to wait quite a bit. You need to follow the main story until night 4 or night 5. Alfred will be at the Belfry and he will tell you that you have an email from Lucius Fox. Once you inspect the email and speak to Alfred, you can find Lucius Fox on the map the next night you’re on patrol.
Head to Lucius Fox’s location and he will tell you about a bat-glider-like vehicle he has. You then need to visit each of the fast travel locations on the map and scan all of the drones in the vicinity. This will unlock that district which you can now fast travel to at any time.