If you need to use an elevator, too bad! It's broken!
Millennium Station serves both Metra Electric and South Shore Line trains, with completely separate platforms for both. Since this is the Metra page, we'll be looking at the Metra platforms.
Metra has their own waiting area for their platforms. Every platform is fully accessible, provided you've made it into the main station somehow!
There's also an entrance from South Water street, which is currently the only accessible way to board Metra Electric in the Loop!
