However with time slipping away, I choose to spend my last week at what many consider to be the best dive area on the mainland, Maria la Gorda on the far western peninsula of the island. Divers here stay at Villa Maria la Gorda, a small, low-key resort with one restaurant and bar and clusters of charming wooden bungalows as well as a block of beach-front rooms. The standard is among the best of any of the places I have stayed in Cuba and rooms are good value at around £30 per night. I book six dives here with the in-house diving centre – approximately £70 for a package, including equipment – it is not even nearly enough, considering there are some 50 sites to explore. The boat goes out three times a day and generally has larger groups though these usually split and head in different directions after reaching the drop-off point.

We enjoy some spectacular dives here, most notably at the Gorgonnese Garden, where we see turtles, stingrays and a large emperorfish along with dense schools of triggerfish, snappers and several morays. Other species of note include boxfish, drumfish, and the diminutive squirrelfish. But our final dive, at the Lost Paradise, is the most breathtaking. After submerging to around 20 metres, we weave through tunnels in the reef to emerge on the other side of a vast coral wall, gazing out into the endless blue.

We drift along the wall for most of the dive, winding through more tunnels at intervals. All of us are lost in our own private worlds, absorbing the visions of pristine, colourful corals and teeming sealife - shoals of turtle-shaped cross-boat fish are silhouetted overhead while queen angelfish, snappers, and triggerfish swarm the reef and large black wrasse, barracuda and black emporers loom out of the blue. Peeking under the corals we observe morays and spidercrabs peering timidly from their holes. I have never seen such an abundance of aquatic life in any one spot, and am mesmerised, left basking in wonderment but sadness when our dive ends.

Yet perhaps our most special encounters in Maria la Gorda take place before we even enter the water. All the divers present are keen to see the sharks - particularly the world's largest fish the whale shark - for which the waters around Cuba are well known. So on each boat trip we scan the horizon eagerly for the patches of white froth which indicate a feeding frenzy, and are twice rewarded our efforts. On the way to our final dive we spy from the top level of the boat a large frenzy, and feeling like pirates who have spotted potential bounty in the distance, direct the boat towards it.

As we approach an enormous fin, perhaps two metres in length, rising out of the water, and all on the boat issue a collective gasp. Getting closer we can see that this is a colossus, at least 10 metres in length, and its awesome majesty leaves us breathless. We cannot get in the water here - swarming for food will be bull sharks and - the most aggressive of them all, including the great white - the tiger. But nevertheless this close encounter - the second but most impressive of my time here - strikes us deeply, leaving us basking in wonderment at the awesome majesty of this docile giant, the king of the seas.

Leaving Maria la Gorda, I am struck, as always at the end of a diving holiday, by an profound sadness that my underwater exploration is over for the time being, and pine for the world which has captivated me for the last weeks. I know, however, that I will be coming back, and that I have so many more places to explore.

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