A veritable sea of people on a typical day at a Paris train station. Or perhaps rats leaving a sinking ship would be a more apt metaphor. Whatever, it's not very pleasant trying to get off and even worse attempting to get on, especially with a touch of mild claustrophobia thrown in for good measure.
Makes you grateful for the times you're able to contemplate the cityscape without millions of people milling around. Try Paris early on a Sunday morning for a taste of what it can be like.