With the winning post in sight, our amateur artists have two nail-biting challenges remaining.With Mariella Frostrup and the Rev. Richard Coles overseeing proceedings, it's the last chance for the finalists to impress the judges with everything they've learned throughout the series.The starting point this week is Queen's House, Greenwich, where we soak up 400 years of history and art in these magnificent surroundings. There is a surprise in store for the artists as they are given their first test: they have to paint a portrait, but their sitters are only revealed to them at the start of the challenge. Will all of our artists be happy with who they come face to face with?For the final challenge of the series, we test not only our artists' skills but also their sea legs - with a trip on the Thames. They are faced with the magnificent view of the Old Royal Naval College in Greenwich – practically unchanged since it inspired Italian master Canaletto over 250 years ago. If that wasn't enough to contend with, mentors Pascal and Diana take a step back to see who has absorbed their artistic advice and who has completely ignored it. Judges Daphne, David and Lachlan have the tricky task of deciding who will be the winner of the Big Painting Challenge 2017.