If you take the Greenwich Meridian as the point separating east from west then these are the extremes that I've been to.
North: Skjervøy, Norway
South: Christchurch, New Zealand
East: Christchurch, New Zealand
West: Papeete, French Polynesia
Then you've got highest and lowest..
Highest: Laguna Miscanti, Chile (4,900m)
Lowest: Dead Sea, Jordan/Israel (-418m)
And a few imaginary lines on the globe.
Crossing them on a plane does not count - only on land!
Tropic of Capricorn: While on a trip in Chile - I've even got a photo of the spot!
Tropic of Cancer: On a sleeper train between Mumbai and Delhi, India - Should it count as I was asleep at the time?
Arctic Circle: On a sleeper train in Norway - I was awake, but couldn't mark the actual crossing spot!