I visited this WHS in December 2015. Sian Ka'an in Mayan means 'Origin of the Sky' and this together with the embossed birdlife reliefs of the Muyil/Chunyaxché ruins hints that the highlight of this natural WHS are mainly birds and mangroves. I tried the route to Punta Allen but decided against visiting after an hour of endless potholes and what was close to offroading. I decided against going all the way mainly because locals informed me that due to the Northerly winds, a lot of waste from cruise ships and from Central America ends up here at this time of year. Instead, I was happy to enjoy the abundant birdlife from the roadside just after 7am (the earlier the better for birdwatching, especially in mangrove sites). Next I headed to the Muyil ruins which open at 8am and just behind the main castillo there is a sacbe and a narrow opening which leads to the Sendero Canan Ha. There was nobody at around 8:15am on Christmas Day so I simply walked on and tried to spot as much birdlife as possible. It is really difficult to spot the rare species among the mangroves but I still managed to spot a Squirrel cuckoo, a pair of Hooded Warblers, Ovenbirds, a motmot and several turkey vultures perched on the high watchtower. Climbing is quite an adventure and the panoramic view of Laguna Muyil and Laguna Chunyaxché is well worth it. The trail leads to a small sandy mangrove beach, where several youngsters offer boat trips to see the mangroves up close and enjoy some drifts. Don't expect to see rare birdlife with such noisy engines. If you're not a completionist or especially if you'll be visiting Rio Lagartos or Rio Celestun during your trip skip this boat trip altogether. I wasn't impressed on the whole and I would classify this natural WHS as a worthy biosphere reserve but with no evident OUV.