The main attraction of Heliopolis is walking. The area around Baron Palace, the Basilica of Notre Dame, and the main arcaded boulevards covers a pleasant 2–3 km loop that takes as long as you want to make it. The streets are wide and the arcades provide shade, making this more walkable than most of central Cairo.
To reach the Obelisk of Senusret I in Matariyya — the ancient monument that predates everything else in the area by three millennia — take a taxi or Uber north (about 3 km). It is not walkable from the main Heliopolis boulevard in comfortable time.
The historic tram is slow but atmospheric if you want to use it for a stretch of the route rather than covering ground quickly.