I visited this WHS just before New Year's Eve 2021 using Ocampo as my base. Already on the highway coming from Morelia there were signs to slow down due to the monarch butterfly migration. Indeed many butterflies are killed each year as roadkill just before the end of the impressive and length migration journey done by the butterflies each year. Ocampo is at an altitude of over 2000 metres so it might be a good idea to rest well before the uphill hike to the butterfly sanctuary if you suffer from altitude sickness. Horse riding tours to the sanctuary are also organised and are a pleasant way of exploring the biosphere reserve. Also, in Ocampo's central plaza, quite a long way from the El Rosario entrance proper, there is the UNESCO WHS inscription plaque.

During peak season, it seems to be normal practice for locals to organise "pacific" demonstrations which in my case meant being obliged to pay some pesos to be allowed access to the road leading up to the El Rosario entrance which was blocked with stones and a rope/chain till I paid the unofficial fee. Moreover, apparently also during peak season, the parking lot for tourists and visitors is some two hundred steps further down now from the upper parking lot used by local vendors, rangers, and the police. Apart from an additional uphill climb up the stairs (and downhill after the visit), you'll be bombarded by local vendors mostly selling the same souvenirs/stuff and repeating the same thing over and over. It really was annoying especially compared to the silent and peaceful atmosphere further up where most of the butterflies stay and flutter around.

At least during our visit, there were no guided tours and also children of any age were allowed to visit. You can also stay in the sanctuary for as long as you like (or till nature calls, since there are no toilets up there). Heeding Nan's advice, I chose to visit just after 12:00 on a hot sunny day, which meant that the butterflies were very active and the uphill hike just after the vendors was like an ascent to the heavens with thousands of butterflies everywhere. I was thrilled by the experience as I thought that such an experience was more likely towards February-March. I also wanted to view them agglomerated on the tree branches and covering the entire bark of the forests of pine and oak, and of drought-resistant oyamel fir trees so I kept on going till a roped off area with signs to keep silent. These trees provide microclimates that provide shelter when temperatures fall to freezing point (quite normal at night but also till late in the morning) or when there are winter rains. Climate change and illegal logging are a constant threat although this year Monarch butterfly numbers have increased again, albeit always staying further up year after year which means a longer hike to get closer. The highest trees were completely covered with Monarch butterflies, so many that some of the smaller branches were bending with the sheer amount of butterflies. As the day progresses and the temperature gets hotter, the rangers move the roped off area further down so as not to disturb the butterflies. The most impressive thing for me was the sound created by the fluttering butterflies as most visitors observe in awe and silence to the spectacle. Some curious butterflies also lay on people's clothes or photography gear (it happened quite a lot of times during our visit).

Overall, a really rewarding visit in one of Mexico's top WHS and UNESCO's top natural WHS.