Arc de Triomphe
The Arc de Triomphe in central Paris is NOT wheelchair accessible.
Yes, they have installed a lift within the Arc de Triomphe itself.
You just need to get there first of all though.
The problem? The Arc de Triomphe sits in the middle of a huge roundabout. And there is no pedestrian crossing above ground (and the traffic is constant and FAST - do NOT NOT NOT try to cross the road here - even if you can walk OK).
Instead, and if you can manage a few steps, pass below the road via the foot tunnel.
And if you can't manage the steps - don't worry. Just view the Arc de Triomphe from across the road (this is the best view OF the Arc de Triomphe anyway). All that you are really missing out on, is the view FROM the top of the Arc de Triomphe (especially the view down the Champs-Élysées to Place de la Concorde and the Louvre beyond - and also the view across to the Eiffel Tower).
But there are much better views over Paris (hint: Tour Montparnasse!!!!).
From memory (and it was a few years ago now), there IS a direct entrance to the Arc de Triomphe from the RER stop here (RER A). However, this might involve steps too? I'll check and update this page when I next visit Paris.