All the way to, as late as: tận

Tận before a place or a time stresses how far or how late: "all the way to", "as late as". Nhà bạn em ở tận Củ Chi, my friend lives all the way out in Củ Chi. It adds the speaker's feeling that the distance or the time is a lot.

For time, it usually comes with tới in Saigon or đến in Hà Nội: tới tận 11 giờ, until as late as 11. Mới often follows to show that the next thing happened only then: Anh làm tới tận 11 giờ mới về, I worked till 11 before I got home.

With places, it follows a verb of going or being: lên tận Đà Lạt, ở tận Củ Chi, ra tận sân bay (all the way out to the airport, to see someone off or pick them up). That kind often shows effort or care.

A few fixed phrases are common in shops and ads: giao hàng tận nhà or tận nơi (delivery right to your door), tận tay (into your own hands).

Without tận, the sentence is neutral: Ba mẹ lên Đà Lạt thăm em just reports the visit. With tận, you hear that they came a long way.