Neak Pean (or Neak Poan) (in Khmer: ប្រាសាទនាគព័ន្ធ) was built by Jayavarman VII in the 12th century as a Buddhist temple.
The site is within a large reservoir (which measured 3500 meters by 900 meters). The walkway takes you to the man made island that contains the Neak Pean temple.
The temple is within the Angkor archaeological park area. I rode my bike between the many large and small temples while living in Siem Reap, Cambodia for a couple months. You can easily see 10 of these small temples and few large ones by bike in one day.
You do get some exercise (which for me was a plus) and it isn’t very hard as the entire area is very flat. Of course the area is also usually hot. You can rent bikes in town for a few US$ a day. You can also rent a tuk tuk or electric bikes.