How do I get through this door to Mr. Freeze?

You should run towards it and when you're close, slide under immediately.

Small gaps like that are too short to crouch under, so you need to perform a running slide.

• On PS3, hold X to run and then press R2 to slide.
• On Xbox 360, hold A to run and then press RT to slide
• On PC, hold Space to run and then press LCtrl to slide.

Pro tip: You can also slide into thugs to trip them up! It's a great way to quickly close the gap on someone who's shooting at you.