Not far outside of Hoi An are a group of ruins, the My Son ruins (pronounced "Me Sun"), which are a series of 70ish ancient Hindu temples for worshiping Shiva, built by the Champa kingdom between the 4th and 13th centuries in a valley surrounded by mountains (although the 20 or so remaining temples were built between the 10th and 13th centuries).
Tim and I took a day trip out to check them out... unfortunately the site is not very well explained by the signs and accompanying museum, so our knowledge is all garnered from the Lonely Planet and the internet.
The temples are in various states of disrepair (or are seemingly currently under repair, as you will see from later photos).
My understanding is that the temples were reclaimed by the jungle after Hinduism waned in the region and the Champa kingdom declined (as the Khmer empire expanded). Restoration by the French began in the 1930s and many of the remaining sculptures were moved to the Museum of Cham Sculpture in Da Nang.
It's actually pretty lucky, in a way, that many of the intact sculptures were moved from My Son to the museum, because during the Vietnam/American war, the Viet Cong used the My Son site as a base, so America carpet-bombed the area in 1969, destroying several of the remaining temples. Some of the unexploded ordnance that was found in the area during/after the war is displayed right next to the artifacts (see below):
Having recently been to some Hindu temples built around the same time, it was pretty interesting for me to see the differences in architectural style, although many of the images and motifs were similar).
You can still see the Sanskrit inscription on this big stone:
Here's some of the restoration (or at least weather protection and structural support) going on at some of the temples:
This is one of the site maps, indicating where each temple is (or was), but also each location where a bomb was dropped (the circles made of triangles show where the bomb crater is):
Sorta hard to see from my photo, but the giant hole in the foreground is one of the bomb craters: