As a way to travel fast, my Earth-like planet is going to have a special train, circling it (the axis of the 'tracks' is aligned with the planet's axis of rotation).
The thing about this train - it never stops and it doesn't end - there is no first or last car, they are all joined in a circle.
Moreover, it's actually several trains, going parallel to each other. The first one travels at the speed of 5 km/h, such that any healthy person can get on it. Then the second train travels at 10 km/h, and they are close enough so it's no trouble to step from one to another. The next travels at 15 km/h, the next at 20 km/h, etc.
I think about 200 trains should be enough to provide the means of fast travel around the planet. Of course, there is the matter of travelling to and from the tracks. As for the 'other side of tracks, we just need a second set of slower and slower trains.
The problems with this concept:
Safety of the passengers. If all the trains function perfectly, then we just need a system of safeguards in place so no one could possibly fall down or injure themselves while stepping between the trains. At the speed difference of 5 km/h even if there are some inner walls or support beams, it still should be safe enough. Now on the other hand, if there is some malfunction, the inertia could kill everyone in the fast moving trains.
Long time functioning of the train. To get rid of friction we could use magnetic tracks (or even tunnel), but it will take a lot of energy. On the other hand, is it possible to use centrifugal force from the fast trains to support the whole structure? How fast should they move in this case (we can make the inner cars heavier than the outer ones)?
What other problems could arise? Interaction with the planet's magnetic field, air resistance currents, etc?
Possible means of building the train: the materials (maybe carbon fiber, like space elevators?), the power, the infrastructure?
(!) Important! The only thing I'm handwaiving is the tracks construction. Let's say we somehow managed to do it, despite the mountains, bodies of water, etc. Maybe under the surface, but I won't elaborate further.
I hope the question is not too broad, I will accept partial answer as well. Probably the only question: how to make this means of travel feasible?
I want to make this believable enough so the real fun about the societal implications could start. Can you imagine working as a conductor on this train?