Sarakhs town was once a stopping point along the Silk Road. Much of the original city site is now just across the border at Saraghs in Turkmenistan.
Mashhad to Sarakhs is 185 km by road and 120 km by train. The border post from Sarakhas / Saraghs are open from 8am to 5pm. No transport goes right across the border, so once through the immigration on the Iranian side get a shuttle (about IR60000) to the Turkmen Immigration post. From there once immigration formalities are complete buses and shared taxis run occasionally to Marv (3 or 4 hours) or Ashgabat (6 hours) from the bus/train station, though transport slows later in the afternoon.