You would be in the Gulf of Guinea, hopefully in a boat, aboat 385 miles south
off the coast of Accra, Ghana. Tourists sail there and take each others' pictures
there, just to say that they've been to the Earth's "zero point". That's nonsense,
of course, because the whole system of latitude and longitude was invented by
people, and the 'zero point' could easily have been somewhere else. The only
points on Earth that are intrinsically unique are the north and south poles.
180° north longitude
The maximum degree of latitude is 90 degrees north and south, so 180 degrees latitude does not exist. If you meant 180 degrees longitude, then the answer would be that the International Date Line, a major line of longitude, is located there.
Australia
20000
The coordinates 15 degrees north latitude and 75 degrees east longitude are located in Asia.
At 80°S and almost ANY longitude, you would be standing on Antarctic ice.
180° north longitude
The prime Meridian is 0 degrees longitude.
The longitude of the State of Missouri is 89 degrees 6'W to 95 degrees 42'W. The Latitude is 36 degrees N to 40 degrees 42'W. The longitude and Latitude of the Missouri River would depend on what location you are researching.
The maximum degree of latitude is 90 degrees north and south, so 180 degrees latitude does not exist. If you meant 180 degrees longitude, then the answer would be that the International Date Line, a major line of longitude, is located there.
Australia
That would be Greenwich.
20000
Since you did not specify the directions of the latitude and longitude lines, the best assumption would be 15 degrees north latitude and 100 degrees east longitude. However, there is no capital city located there, and none at the other combinations. It is actually Chainat province in Thailand.
The coordinates 15 degrees north latitude and 75 degrees east longitude are located in Asia.
In the middle of the Pacific
technically sea but near Indonesia