Samsara literally means "wandering-on." Many people think of it as the Buddhist name for the place where we currently live — the place we leave when we go to nibbana. But in the early Buddhist texts, it's the answer, not to the question, "Where are we?" but to the question, "What are we doing?" Instead of a place, it's a process: the tendency to keep creating worlds and then moving into them. As one world falls apart, you create another one and go there. At the same time, you bump into other people who are creating their own worlds, too.
The play and creativity in the process can sometimes be enjoyable. In fact, it would be perfectly innocuous if it didn't entail so much suffering. The worlds we create keep caving in and killing us. Moving into a new world requires effort: not only the pains and risks of taking birth, but also the hard knocks — mental and physical — that come from going through childhood into adulthood, over and over again. The Buddha once asked his monks, "Which do you think is greater: the water in the oceans or the tears you've shed while wandering on?" His answer: the tears. Think of that the next time you gaze at the ocean or play in its waves.
In addition to creating suffering for ourselves, the worlds we create feed off the worlds of others, just as theirs feed off ours. In some cases the feeding may be mutually enjoyable and beneficial, but even then the arrangement has to come to an end. More typically, it causes harm to at least one side of the relationship, often to both. When you think of all the suffering that goes into keeping just one person clothed, fed, sheltered, and healthy — the suffering both for those who have to pay for these requisites, as well as those who have to labor or die in their production — you see how exploitative even the most rudimentary process of world-building can be.
This is why the Buddha tried to find the way to stop samsara-ing. Once he had found it, he encouraged others to follow it, too. Because samsara-ing is something that each of us does, each of us has to stop it him or her self alone. If samsara were a place, it might seem selfish for one person to look for an escape, leaving others behind. But when you realize that it's a process, there's nothing selfish about stopping it at all. It's like giving up an addiction or an abusive habit. When you learn the skills needed to stop creating your own worlds of suffering, you can share those skills with others so that they can stop creating theirs. At the same time, you'll never have to feed off the worlds of others, so to that extent you're lightening their load as well.
It's true that the Buddha likened the practice for stopping samsara to the act of going from one place to another: from this side of a river to the further shore. But the passages where he makes this comparison often end with a paradox: the further shore has no "here," no "there," no "in between." From that perspective, it's obvious that samsara's parameters of space and time were not the pre-existing context in which we wandered. They were the result of our wandering.
For someone addicted to world-building, the lack of familiar parameters sounds unsettling. But if you're tired of creating incessant, unnecessary suffering, you might want to give it a try. After all, you could always resume building if the lack of "here" or "there" turned out to be dull. But of those who have learned how to break the habit, no one has ever felt tempted to samsara again.