Stand on the equator
Put one foot in the Northern Hemisphere and the other in the Southern. The equator crosses thirteen countries and thousands of kilometres of ocean, with marked visitor sites in places including Ecuador, Uganda, Kenya and Indonesia. Some monuments are ceremonial rather than survey-perfect, which makes checking the actual line part of the fun. The experience can be a quick roadside photograph or the organising idea for a much bigger journey. At a well-run centre you may find displays about latitude, local geography and the way satellite measurements refined older markers. Ignore demonstrations that claim the Coriolis effect can be proved by moving a bowl a few metres; at that scale, technique matters far more than hemisphere. Choose an established, safely accessible marker and confirm opening arrangements before travelling. Carry sun protection and water, respect local communities and save an offline map if the site is remote. Add this to your list and occupy both halves of the planet for one wonderfully literal moment.