Help me find a book describing two specific walks across Paris, France

I once had a small book (in French) that covered two approx. half-day walks across Paris, France.

• One went north-to-south: it perhaps started at a science museum up north and ended at a university campus down south.
• The other went east to west: it perhaps started and ended at two of the large parks in the east and west of town respectively.

I did them both (more than a decade ago), but can no longer remember the book's title. The book was specifically on this topic and it may have been from a (semi-)official source, such as a French national geographic society.

Can anybody tell its title or point me to other information (perhaps even an app, nowadays) about those two walks?