The easiest and most popular area for trekking is in the northwest mountains around Sa Pa and, to a lesser extent, Mai Chau. Sa Pa is also the starting point for ascents of the country’s highest peak, Fan Si Pan, a challenge to be undertaken only by experienced hikers. Other options include hiking around Kon Tum or Da Lat in the central highlands or in one of Vietnam’s many national parks, including Cat Ba, Cuc Phuong, Bach Ma, Cat Tien and Yok Don. In Yok Don you can even go elephant trekking.
There’s no problem about striking out on your own for a day’s hiking. However, for anything more adventurous, particularly if you want to overnight in the villages, you’ll need to make arrangements in advance. This is easily done either before you arrive in Vietnam or through local tour agents, most of which offer organized tours and tailor-made packages. Note that it’s essential to take a guide if you are keen to get off the beaten track: many areas are still sensitive about the presence of foreigners.
More Detail Trekking Tours at : http://www.indochinaexploretours.com/category/vietnam-trekking-tours/