The Chulachomklao Fort (ป้อมพระจุลจอมเกล้า) is located at the mouth of the Chao Phraya River. Though the area is still used by the Royal Thai Navy, the historical fort part is open for visitors.
The site can be divided into three parts. At the center is the statue of King Rama V, in the west usually known as Chulalongkorn, while Chulachomklao is another part of his full royal title. Around the statue is a small park, and in the pedestal of the statue is a small museum on the history of the site. Sadly I failed to go inside that one as I did not know about it then, though I noticed the door behind the statue opposite to the entrance into the fortified parts.
South of the statue are the fortified parts. Entering at the statue, one directly stand inside on a walkway. The doors lead to the actual purpose of the whole building - hosting the large Armstrong cannons - as well as auxiliary rooms like ammunition storage.
These cannons were installed shortly after the fort was completed in 1892. The King ordered a total of 10 cannons, of which three were planned to this fort. Already the following year they went into action for the first and only time, when the French sloop Inconstant and gunboat Comete entered the Chao Phraya despite not getting allowance for the entrance. However the cannons failed to stop the boats, thus the French could use this incident now know as the Paknam Incident to force Siam to cease modern-day Laos to French Indochina.
Another highlight of the site is the HTMS Maeklong. This former escort vessel and training ship is now permanently moored at the fort, and can also be entered. It is really interesting to climb up and down the ladders, see inside the former crew quarters, the bridge or the cannons on board. All of course quite old - the ship was build in 1936, and decommissioned in 1995.
Another thing I apparently missed during my visit is a boardwalk into the mangrove, which can be used for some bird watching.