Malaysia is ramping up efforts to search for an Indian tourist who fell into a sinkhole in Kuala Lumpur last Friday (Aug 23), and has formed a task force to inspect sewage pipes and to assess the safety of structures. There are worries about soil instability after a second sinkhole emerged about 50 meters away. What should we know about sinkholes? Is Kuala Lumpur still safe to visit? Associate Professor Wu Wei from NTU School of Civil and Environmental Engineering explains what causes a sinkhole and the technologies that can mitigate sinkhole risks and damage.