Complex sentence: The structure is believed to have been constructed in 8th Century AD, when Adi Shankara visited this place and the present structure is on a site adjacent to the site where Pandavas are believed to have built the temple.
Split into simpler sentences: The structure is believed to have been constructed in the 8th century AD, when Adi Shankara visited. The present structure is on a site adjacent to where Pandavas are believed to have built the temple.