The best way to develop your skills and increase your experience, is the PADI Advanced Open Water course. In this course you will make 5 dives, including a navigation dive and a deep dive. The other 3 dives you can determine with your Instructor. Think of wreck diving, underwater photography, fish recognition, peak performance buoyancy etc. There is a theory chapter for each dive, but it’s not a lot and there’s no exam. Learning by doing!
This course costs 310€ plus 49€ if you need to rent full diving equipment.