To really get away from it all, head to Molimo-Nthuse (the name translates as God-Help-Me Pass.) The views are great, and the hiking is pleasant, albeit very basic.
The government's Pony Trekking Center is there and can help you arrange treks of up to five days. There are no lodges, restaurants or stores, so you'll need to take a tent and all provisions with you. For catered (and correspondingly pricier) treks, contact the lodges in Malealea or Semonkong.
60 mi/100 km east of Maseru.