A stones throw away from our hostel is the Phra Sumen Fort and Santichaiprakan park. We stumbled across it really as we were heading out for a bite to eat, but the fort really does stand out from the rest of the surroundings.
It is an 8 sided, 18th C fort aimed to defend against potential naval invasions. I am not sure that it is possible to enter it, as we didn’t really try as it looks more run down then the other wats and buildings we visited in Bangkok.
Alongside the fort is Santichaiprakan park. It is a small grassy area on the riverside, where students and teenaged hang out. We find see a rather energetic aerobic class taking place one night- not that we were persuaded to have a go!