Obviously in order to do the following you need to have the money so this is just a hypothetical, but:
Could I right now book a flight from the UK to, say, Canada or Australia or the USA for literally tomorrow or two days’ time and just go?
Like, if I had the money and the time, would I be able to go or is there anything else you have to do?
Also, could I theoretically like fly from London to NYC on one day and then fly back within hours?
Obviously, nobody would do that - but I’m just cultus if you’re allowed to do that