Cascais, Portugal (PT)
This type of fishing generally requires a decent amount of travelling away from land. You will be fishing in potentially large depths of water but generally chasing tuna or marlin type species that live closer to the surface. Famous pioneers like Ernest Hemingway made deep sea fishing and big game fishing very popular. For deep sea fishing large, expensive boats and strong fishing tackle are required.
With the need to be in the deep waters a boat is an obvious requirement for deep-sea fishing. You will also potentially use a game chair onboard the boat to assist with landing the game fish you are targetting. A strong rod, reel and line combination is also just as important.