Hydra is great but it does take a bit of time and effort to get to from the Cyclades. You’ll need to ferry to Athens, then might have to overnight there, then ferry to Hydra. Whereas Naxos, Paros, Milos, Folegandros, etc. would all be one direct ferry from Santorini or Mykonos. If you do go to Hydra then Leto Hotel is a great choice close to the port and shops and restaurants.
Naturally, there are some amazing coral reefs for snorkeling and diving and pristine beaches (my favorite is Whitehaven Beach). Upon arrival, you’ll instantly see why this is one of the best tropical islands in the world — and why over half a million people visit a year. One of the most popular way to see the islands is via a multi-day sailing tour (which is what I did when I visited). It was an amazing experience — especially diving! Prices start around 450 AUD for multi-day sailing tours.
By the early 1920s, small airlines were struggling to compete, and there was a movement towards increased rationalization and consolidation. In 1924, Imperial Airways was formed from the merger of Instone Air Line Company, British Marine Air Navigation, Daimler Airway and Handley Page Transport Co Ltd., to allow British airlines to compete with stiff competition from French and German airlines that were enjoying heavy government subsidies. The airline was a pioneer in surveying and opening up air routes across the world to serve far-flung parts of the British Empire and to enhance trade and integration.