Complex sentence: It should not be confused with the northern part of the Greenwich peninsula, formerly known as "East Greenwich" that lies south of the river on the Blackwall peninsula, and is the site of the Millennium Dome.
Split into simpler sentences: It should not be confused with the northern part of present-day Greenwich. However, this is not in the area historically known as North Greenwich, but rather is south of the river on the Blackwall peninsula, also known as the Greenwich peninsula, near the Millennium Dome.