Daugavgrīva Castle (German: Dünamünde; Polish: Dynemunt; Russian: Усть-Двинск or Ust`-Dvinsk) is a former monastery converted into a castle, located at Vecdaugava oxbow on right bank of Daugava, in the northern part of Riga city, in the Vidzeme region of Latvia.

During a raid of tribal Curonians in 1228,[1] the monastery and its tombs were destroyed, although the monks rebuilt the abbey after fighting died down.

In 1305, the local abbot sold the monastery to the Livonian Branch of the Teutonic Knights, who began construction of the fortress of Dünamünde.

In 1481, the knights closed the Daugava to navigation by stretching an iron chain from Dünamünde to the opposite riverbank, thus hoping to ruin Riga's trade.

Because Riga itself was controlled by the Archbishops, the local administrative seat (Komturei) of the monastic state of the Teutonic Knights was located in Dünamünde.