> Travelling around the Universe would take forever even at the speed of light.

If we're talking about traveling within our galaxy; the distances and thus sub-light travel times involved are huge, however the time spans available are even huger.

On the timescale of planets, a million years is not "forever" but actually a quite trivial amount of time - if there was an almost perfect clone of Earth on the other side of Milky Way where the evolution of multicellular life happened 1% faster than it did here, then they would be tens of millions of years ahead of us, and that is not only enough to reach us at speeds much lower than c but also enough to colonize the whole galaxy while doing so, spending multiple millenia at each planet before moving on.

To be fair about what has been in progress, we have the theoretical possibility of traveling through wormholes, which would allow "traveling" faster than light (well not really going faster than C but simply distorting spacetime itself to reach a point that would require traveling faster than C if we were to travel without distortion) yet there are many practical problems around it.

Of course this doesn't mean that some advanced civilization haven't figured out how to practically use it, which I'm sure we'll also discover (in distant future) if we aren't killed by something else (most likely ourselves).

>Travelling around the Universe would take forever even at the speed of light.

It’s even worse than that. Since universe is expanding, there is limited area that is possible to reach with the speed of light. In 200 billion years other galaxies are not going to be visible anymore.

Yup. There was a famous talk with a astrophysicst (forgot who and the name of the talk) where he was demonstrating this in an ELI5 manner which made perfect sense.

He was saying in the future even with the greatest advancements of technology and telescopes if they look at the sky they won't ever see anything and there will be no clue of there were other galaxies (or clusters, not sure) ever, because of expansion and redshift.

It’s depressing. All this stuff that we will never ever be able to explore, and won’t even know exists at some point. I’m not even remotely religious, but sometimes I like to think that after death, we still continue to exist, but free from the constraints of physics, so we can explore the whole universe, through all of space and time.

Unless those aliens are close. There are a few stars within 5 light years, it seems reasonable that a sufficiently advanced civilization could reach us from that close in a reasonable amount of time. if they are really long lived 100 light years seems like the outside edge of reasonable travel distance.

Why do you think 100 light years is the edge of "reasonable travel distance"? I put to you that you are imposing your human standards on other species, assuming that what seems to you to be a long time would also be a long time to another species.

Maybe the aliens have an average livespan of 200k Earth-years. Maybe much more. Maybe they experience time differently, and for them a 100 year journey feels to them like a walk around the block.

100 light years is arbitrary, but even for long lives things it seems like too far - few things on earth are that long lived, and bodies do break down over time, as do spaceships.

Until we know the entire universe (because of the way the universe is expanding this is impossible) we cannot do more than apply our best guess, but I think I hit a good upper limit. Even if I'm off I seems unlikely it is by much.