Sebyeonggwan was the command hall of the Three Provinces Naval Headquarters, built in 1605 after the Imjin War. It is broad, low, and severe rather than ornate, which suits its purpose: this was a place of military administration, not court display.
The hall gives Tongyeong's Admiral Yi story a real setting. Stand in front of it, then walk back toward the harbour and the geography of the old naval base starts to make sense.