The slope was 'challenging' for even the most experienced climbers.
A number of doctors are 'challenging' the study's claims.
It's a 'challenging' book that requires careful reading.
(..) This is a major remodel, you know! This is a disaster! Was it programmed to stop before it took my head off? Ah, well... that would be a "no". - But you said, "Make it more challenging." - Hence, the live fire. Live rounds again. Poor Simon! What has she done to you? - Very funny. (..)2001 Lara Croft: Tomb Raider