Zanzibar and its surrounding islands lie at the heart of a busy shipping lane. But what boats sailing these waters can’t see are the treacherous reefs that lie below. Many ships have been wrecked in the past and these days there is a series of lighthouses to warn unsuspecting sailors. But there’s one island without a lighthouse and that’s Bawe, so this week the team’s challenge is to build one.

If building a lighthouse wasn’t a big enough challenge, the uninhabited island of Bawe is an hour’s journey from the mainland and covered by dense tropical forest. There’s no electricity, as Kathy finds out when she goes to recce the island to find a good spot for the team to site their construction.

Ellen and Mike need to make a light that will be visible from far out to sea.

Jonathan and Ellen have the job of making the lighthouse structure and inventing a mechanism to make the light flash and Kathy has the job of making it turn. She decides to rely on rock power…but her ideas don’t quite go to plan.

We’ll find out whether or not they’ve succeeded on the evening of day three when we take a trip past the island after dusk.