Quick answer: The Yellow Bridge is a narrow suspension bridge for people and scooters that joins Lembongan to Nusa Ceningan. The old one collapsed in 2016; the new one opened in February 2017. On the other side are the Blue Lagoon and Secret Beach.
Nusa Ceningan is the small island between Lembongan and Penida. It's connected to Lembongan by the Yellow Bridge, a narrow suspension bridge across the mangrove and seaweed channel, so you can reach it on foot, by bicycle or by scooter.
The bridge
The bridge is a local landmark, painted yellow, and only wide enough for people and scooters. The old bridge collapsed on 16 October 2016, overloaded with people on their way to a ceremony. Eight people died and dozens were injured. A new bridge opened in February 2017. Cross slowly, give way, and don't stop in the middle for photos when it's busy.
Below the bridge is the channel where seaweed is farmed in the shallows. At low tide you can see the plots and the farmers working them. More on the seaweed farms.

Blue Lagoon
On Ceningan's west side, a deep cove ringed by limestone cliffs, with water so blue it looks dyed. It's a viewpoint first. People do jump from the cliffs here, but the swell can be powerful: only when locals say the sea is calm, never alone, and never at low tide. Blue Lagoon and Mahana Point.
Secret Beach
A small, quiet cove on Ceningan, reached down a short path. Lovely when the sea is calm; the waves can be strong when it isn't.
The roads
Ceningan's roads are narrow, steep and in places rough. If you are not confident on a scooter, this is not the place to learn. Walking or a bicycle on the flatter stretches is fine.
Questions
Can you drive across the Yellow Bridge?
On foot, by bicycle or by scooter only. It is a narrow suspension bridge, not for cars.
What happened to the Yellow Bridge?
The old bridge collapsed on 16 October 2016, overloaded during a religious ceremony. Eight people died and dozens were injured. A new bridge, about 140 metres long, opened in February 2017.
Is Nusa Ceningan worth visiting?
Yes. It is small and quiet, with the Blue Lagoon, Secret Beach, cliff views and the seaweed channel. Half a day is enough to see the highlights.
Is cliff jumping at the Blue Lagoon safe?
Only when the sea is calm and locals say it's fine, never alone and never at low tide. The swell can be powerful.
Header photo: Juxlos, CC BY-SA 4.0, via Wikimedia Commons
Devil's Tears and Dream Beach
The mangroves