I visited this tentative WHS in March 2018 as part of my day trip covering most of the Meknes hotspot. Just before noon, I drove up to the highest hill looking over the hill where Moulay Idriss Zerhoun is perched beneath Mount Zerhoun.
On the day of my visit (a Saturday), there was a huge car boot sale and market going on so driving my rental car uphill through the narrow streets packed with locals, improvised stalls and donkeys was quite a challenge. The panoramic view from the top though was well worth it and helped me find my bearings afterwards from one alley to the next around the mosque area (open only to muslims). The experience was quite similar to the medina of Tetouan but here the whole focus of most locals and visitors is on religion.
For Moroccans, six pilgrimages to Moulay Idriss Zerhoun during the annual festival honoring Moulay Idriss is equivalent to one Hajj to Mecca. In 789, Moulay Idriss I arrived in Morocco bringing Islam to Morocco and starting a new dynasty. In addition to founding the sacred town named after him, he also initiated the construction of Fes, continued later by his son, Moulay Idriss II.
Therefore, the heart of this town is the Mausoleum of Moulay Idriss I accessible only to muslims. A quick peek (photo) just off the main square will still give you a gorgeous view of the central courtyard and minaret. I spent most of my time here watching pilgrims from all walks of life entering/exiting the mausoleum. Another minaret worth viewing, is the green one further away, the only round one in Morocco. It reminded me of a similar but older one present in Male, Maldives.