This is a historic place to visit, as it's the resting place of CHINA'S first Emperor, it's about 5km before you get to the Terracotta Worriors, well worth the stop. Do it on the way out as it will give you a better understanding of the Terracotta Army, there is a great 1/2hr Stage Show every 2hr's, than you can walk to the top of the hill/mausoleum which gives you a great view of the surrounding country, you can also see the site of the Terracotta Army some 5km away.
P.S dont bother taking the Golf Buggy Tour, it only takes you around the Pine tree plantation and to a small Fortune Telling site where they try to extract more money from you.
Other than that this is a great place to see.