The PADI Semiclosed Rebreather Course
If novelty and diving quietly appeal to to you, then try the Semiclosed Rebreather course.

The Fun Part
The main feature of a semiclosed rebreather is the reduced bubbles and silence it offers, which allows you to get closer to shy wildlife.

What You Learn
Through the Semiclosed Rebreather Specialty course you learn the special procedures for semiclosed rebreather scuba diving. This includes special dive planning, organisation, procedures and potential hazards, many of which differ significantly from conventional (open circuit) scuba.

It specifically focuses on the features, accessories, maintenance and proper use of the Draeger Semi-closed Rebreather. You make at least one confined water dive and at least three open water dives to learn:

Advantages and disadvantages of the rebreather
Assembly, disassembly and maintenance
Dive planning and emergency procedures with semiclosed rebreathers
The Scuba Gear You Use
You get to try the semiclosed rebreather, of course. You also need your  mask, fins, snorkel, weight system and wetsuit /drysuit.
All available from Dive Central.

Prerequisites
You must be a
PADI Advanced Open Water Diver (or qualifying certification from another organisation) or a PADI Open Water Diver (or qualifying certification from another organisation) with proof of at least 10 logged dives beyond open water training dives
PADI Enriched Air Diver (or qualifying certification from another organisation)
 

The cost of your Semi Closed Re-Breather Course is £600