Just like you, but different
The more you think about it the more down a rabbit hole you go. I’ve moved on from how is there gravity in spaceships and celestial navigation to more mundane things.
And the answers it seems are
You can check out the maps here The pins are the closest land-fall point, there are some opposites that pop out in the middle of the sea.
The opposite side of the world to London is Portobello, Otago, New Zealand. – actually it isn’t it’s 922km out to sea.
The opposite side of the world to Los Angeles is Saint-Philippe, Reunion, Reunion.
The opposite side of the world to San Francisco is that well known tourist destination of Port-aux-Français, Kerguelen, French Southern Territories.
The opposite side of the world to Jacksonville is Kalbarri, Western Australia, Australia give or take.
So, I have the mass that might attract a 1Kg weight, I’d weigh nothing in the middle of the earth, and 40 minutes for a through the earth transit, however some of the opposite sides end in the middle of the sea.
And with that I went to sleep.