Capital of the same named Cambodian province
Doun Kaev, seat of Takeav (or Takeo Province), is a small city of about 40,000 in the Mekong Lowlands and Central Plains south of Phnom Penh.
In Doun Praev there is a strong cottage industry of silk weaving where in fact most of Cambodia's silk product is produced. Here you are really out in the middle of rice paddies, hot and sticky, and you'd probably just as soon be getting on to Krong Kaeb or maybe Vietnam, but there are two sites worth seeing. In that context, don't necessarily go to Doun Praev, because it's not on the way to either of these. It's just used to categorize these sites since that's the district in which they fall (see directions below instead).
Probably most conveniently, just drive or arrange transport down Hwy 2 from Phnom Penh. It's a straight shot. There may be a ferry service of sorts between Doun Kaev and destinations along the Mekong River, but that is likely to be a bit time-consuming and involved logistically-speaking.
Most definitely you are going to need motorized transport to see the sites listed below, or a bike at least, if you're really intrepid, since they are out in the country.
Little eateries along the way
Probably you're going to want to just make this a day outing, but there is a pretty nice casino resort in Chrey Thum close to Phnom Da on the Vietnam border, which will soon be accompanied by another casino resort called Yong Yuan once it is completed.