With the winning post in sight, the 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 is Queen's House, Greenwich, where there's 400 years of history and art to soak up in the 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 the artists be happy with who they come face to face with?For the final challenge of the series, not only are the artists' skills put to the test 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 Anson and Diana Ali take a step back to see who has absorbed their artistic advice and who will completely ignore it. Judges Daphne Todd, David Dibosa and Lachlan Goudie have the tricky task of deciding who will be the winner of the Big Painting Challenge 2017.