Bro cupid xpress
For Vung Tau, head straight to the hotels which has massage/saunas...the ones I have been to offer not only the usual HJ or BJ but the full job...but beware as the cost of damage is more expensive than the city...alternatively, if you can find a local Vietnamese friend who knows Vung Tau well, then ho sei liao...they know how to find girls to come to your room - 800,000 dong for one night...but dun expect model-looks lah!
Other than that, enjoy Vung Tau and just prepare to fork out a wee more for the taxis there with their meters heading north happily and faster than those in Saigon.
