Nowhere is an empty white void which is visited by Squidward in "SB-129." After being chased out of the past by Primitive Sponge and Primitive Star, the time machine he travels goes haywire, after he broke the switch, and transports him to this white wasteland of loneliness. He seems happy to have a place all to himself, but after an echoing of the word "alone," he attempts to escape and only does so because he begs the time machine to take him home after admitting he misses SpongeBob as well as his Easter Island head and Bikini Bottom. Apparently, it is right above the time machine.
At first glance, there appears to be nothing at first, but walking down a bit further reveals some different colored squares that can be lifted up, but disappear after doing so, and the squares can be seen on the floor and ceiling. Also, there are some strange voices that can be heard and every sound heard is echoed, that also includes the sound of one's voice and those same odd voices seem to repeat what one says (e.g., when Squidward said "Alone!" many other voices echoed back "Alone...") and if that wasn't enough, there are speech bubbles that seem to pop out of nowhere. Besides the squares, there seems to be absolutely nothing else at all, nothing physical, no trace of life, just plain emptiness that seems to go on forever (when Squidward tried running through it, he kept looping back to where he started). An interesting thing to note is that it seems breathable for creatures who normally need water in order to breathe, an obvious example being Squidward, when there doesn't seem to be any water at all. There seems to be no exit out of this place of eternal loneliness since running around loops you back to the original location (the only reason Squidward escaped is because he begged the time machine to take him home and it was lucky for him the machine was under his feet, perhaps the entire time). It can be assumed absolutely nothing or nobody is here because it is the end of time.
When Squidward first enters here, he seems to be the only thing visible in this lonely place. As he walks along further, he finds square tiles that he can lift up. After summing up that SpongeBob and Patrick are nowhere within sight, he relishes in the fact that he found a place where he can be all to himself and with nobody else around (in the background there is a pink square and a yellow square that may resemble SpongeBob and Patrick). However, after he hears many voices echo "Alone..." he attempts to get out by running. That proves futile because Squidward keeps ending up right back to where he started from. After looping back 4 times, Squidward notices the time machine's is nowhere, and wonders where anything is. After stomping the floor 4 times (as well as shouting "Where?!" 4 times), he finds the time machine again after falling through its ceiling. Squidward then finally breaks down, begs to go home, and admits he misses SpongeBob. After he speaks the final sentence, Squidward is finally able to escape the realm.