The Basilica of the Sacred Heart of Paris, better known as just Sacré-Cœur, is a Roman Catholic church which sits at the summit of the butte Montmartre and is the highest point in the city. It can also be accessed by a Funicular (which will only cost you a metro ticket) if you don't feel like climbing anymore stairs (no judgement here guys).
Even if you don’t enter the actual Basilica, you will still want to admire the view from the steps of Sacré-Cœur. While you’re up there, try to pick out some of Paris’ famous landmarks. Hint, you won’t see the Eiffel Tower from here but you can spot another very famous church and just beyond that, the Pantheon.
If you want to see the Eiffel Tower, walk past the top of the Funicular (so it’s on your left) and follow the fence. From here, if you peak between the iron posts, you can see the Eiffel Tower across the rooftops.
And if you happen to be visiting during the summer months, you will most likely enjoy some live music and entertainment during your sunset!