An area known near the florida islands near the gulf of mexico. The area varies by shape every year but remains in a triangular shape.
Many ships and aircraft, most famous are Flight 17 (the US AirForce bomber squad that vanished during trainig excersizes) and the USS Cyclops (the refueling ship that disappeared along with 309 US crewmen, many scientists believe that since the earth rotates on an axis of roughly 23 degrees which can lead to a wormhole effect/portal which can spontaneously occur at any place on earth or space. There is also another theory that states the ocean currents of the earth are determined by the amount of energy from the sun and the gravitational pull and spin of the earth, which can lead to accumlated deposits solar energy (ie dark energy) which is what is believed to power these wormholes/portals. Since the main atlantic current speeds up to about 8 knots and runs through the area known as the Bermuda Triangle, this can lead one to believe that these missing vessels may have been teleported to another dimension.
Most of the accidents/disappearances ocurred in the early 1900s when radar,sonar, and communications were in the early stages of development which can lead to the posiblilty that human error is the result of these accidents. Like explained earlier, the atlantic current is really strong in this particular area of the atlantic sea, many storms and hurricanes occur there often which can lead many to believe that these ships and aircraft were lost at sea during fierce storms and hurricanes.
Note- No theory of the bermuda triangle has been proven or disproven, many scientists are starting to believe that paranormal activity and parallel dimensions are a posibility, however will have to wait until the technology catchs up to find out.