Take the metro to Pere-Lachaise cemetery to see amazing array of tombs dating back centuries - Edith Piaf, Jim Morrison, Oscar Wilde and Colette to name a few.
Plus amazing war and concentration camp memorials. Peaceful, beautiful, and inspiring in a weird way. An opportunity to refine your thoughts on what you would like your eventual memorial to be.
Get off the metro at Gambetta for the entrance closer to more modern dead. Pere-Lachaise stop for the more historical monuments.