Châtelet-Les Halles is the biggest metro interchange in Paris and it's a nightmare if you don't know the layout. Here's what actually works:

Follow destination station signs, not line numbers. The station has multiple levels and you can waste 10 minutes walking in circles. Exit signs are better markers than platform signs.

RER to metro transfers: go up one level first, then follow directional signs. Don't try to go directly — You'll get lost in the shopping mall section. Line 14 platform is the deepest and takes 5 minutes just to reach.

Rush hour timing: 8-9am, 6-7pm. Allow extra time. This station gets genuinely crowded and escalators break down regularly.