this temple with a gigantic stupa is one of my few favorite buddhist monuments in thailand. the giant size of the stupa is amazing. it can be seen from almost anywhere within the city. the standing buddha image at the main entrance is considered the main attraction. it attracts pilgrims as well as tourists from everywhere here. the outer ring of the stupa's base is well decorated and worth a walk around. if you are here on weekdays, you may observe the buddhist school at this temple with teachers and students here are monks and novices.
the best thing here that you can hardly find anywhere in the touristy thailand nowaday is the lack of mass tourism. Nakon Pathom is not a popular destination for international tourists. not many of them know or are interested in visiting phra patom chedi. 95% of the visitors here are locals. it is truly a hidden gem.
so, enjoy it.