A planet some forty thousand light-years from Sikaris, visited in moments by Harry Kim and Eudana using the Sikarians' spatial trajector.
Alastria is a planet seen briefly in the Voyager episode Prime Factors.
While Voyager's crew enjoy the hospitality of Sikaris, Harry Kim spends time with a young woman named Eudana. She invites him to step on to a platform with her, and they arrive on a windswept shore under two suns. Kim realises that this cannot be Sikaris, and Eudana tells him it is Alastria, forty thousand light-years away.
The discovery that the Sikarians can fold space over such distances offers a way to cut Voyager's journey in half. Their law forbids sharing the technology, which leads Torres, Seska and finally Tuvok to obtain it behind Janeway's back.