Mahakan Fort is the easternmost fort of Rattanakosin's walls, now situated next to Phan Fa Lilat Bridge of Ratchadamnoen Avenue and the junction of Khlong Maha Nak (the beginning of Saen Saep Canal) and Khlong Rop Krung. The fort, also octagonal in shape and in three levels, has a diameter of 38 metres (125 ft) and a height of 19 metres (62 ft), measured to the roof of the octagonal tower. Mahakan Fort has rectangular battlements on both its lower and upper levels, while the connected 180-metre (590 ft)-long section of the city walls features sema-shaped battlements. The fort and walls were also restored in 1981 for the city's bicentennial.

Along with Phra Sumen Fort, Mahakan is one of two remaining citadels out of the original 14 that were built around Rattanakosin Island back when invasions from Burmese and other armies were a constant threat. The octagonal fortress has three tiers rising to a guard post. Cannons placed around the thick outer walls now loom over the surrounding footpaths.

Near Mahakan Fort, between the city wall and the canal, lies an old community whose wooden houses serve as an example of historic vernacular architecture. The community has been engaged in a decades-long struggle against eviction by the BMA, which intends to develop the area as a public park. Although agreements had been made in the 2000s to preserve and develop the neighbourhood as a living museum, the deals later broke down, and the BMA began demolishing houses whose owners accepted compensation in 2016. Other residents are still resisting eviction as of 2017, and there are still hopes that some of the buildings will be preserved. As of April 2018, all remaining residents have been evicted, and plans are underway to tear the remaining buildings down. However, the Mahakan Fort Community’s Facebook page has announced an initiative to create an online database about the Mahakan Fort community, and is crowdsourcing information about the site. In July 2018, BMA was completely developed surrounding area of Mahakan Fort to become a public park and the fort exhibition.