In the Lenggong Valley I have visited in this order the Tasik Raban, Archeological Museum, Gua Ngaum, another cave close to Gua Ngaum, Bukit Jawa und Gua Badak. To my understanding and according to the maps on unesco website and in the archeological museum all of the places except Tasik Raban should be in the buffer zone and the cave (Gua) Ngaum and its neighbouring caves, the museum and Bukit Jawa should also be in the core zone of the WHS. 
 
We took the guide Chou Z Lam that our host in Kuala Kangsar recommended and I would also recommend him (WhatsApp: +60 11-1083 2046). He had a car.  
 
We stopped first at Tasik Raban, a huge lake that is fed by the Perak river. It´s a nice lake and interesting for its geologic history. We saw some snails, fish and a monitor lizard swimming in it.  The second stop was the museum that seems big but only 1 room was open. There is a replica of the Perak man, a almost complete 10,000 year old skeleton, that was found in one of the many caves around as well as some information on tools that have been found, the excavation process and the process of becoming a world heritage site. It´s good to visit the museum as it gives some context and you´re already in the core zone of the WHS.  
 
From Kampung Masjid north of Lenggong town we took to hikes in the hot weather and in the partially muddy forest to visit two different caves- the Ngaum cave and the cave that is called bat cave in Malay (forgot the name). The second one is protected by a fence that was open luckily. The Ngaum cave is accessible. Originally I wanted to visit the Kajang cave, however you need to apply for permit three days in advance and my guide did not want to violate the process. Also he said it´s protected by a fence as well and he already experienced visiting it with permit and still the fence was locked. Clear criticism of the handling of tourists in this case by him as well. In the Ngaum cave you can walk quite deep inside and many bats fly around. Both caves had excavation holes, some with labels, in their entrances. Afterwards we drove to Bukit Jawa where formerly the river has been flowing and some tools were left at the former river bank. Today the river flows 72 meters deeper in the valley. There is nothing much to see other than a hole in the floor, a roof for protection for tourists and a short explanation text. Finally we visited the cave Gua Badak which is close to Gua Harimau and has some cave paintings that are hard to see today but where much clearer 100 years ago when a British guy took pictures of them.(see picture) It´s not related to the WHS directly and also I always struggle a bit with cave paintings especially when they have not been analysed by experts like these ones. Are they real and how old are they? Our guide had some theories but well.  
 
Worth to mention that I had the idea to do the visit from Kuala Kangsar by public transport. I think it´s possible but tough and not worth the extra effort. The tour was 120 MYR p.p.. The bus schedule of the bus that goes into the valley (nr. 99) you find here: https://peraktransit.com.my/routes-2/#pt_stage_bus. However if you want to visit the different components you must either walk a lot in the heat or wait long times for the bus to change location. Also with a rental car from a bigger city it can be an option. 
 
I can recommend to stay in Kuala Kangsar and also visit the royal mosque there and get a short view of the huge royal palace. The Garden resort of Jesmond was a convenient place to stay and the owner will bring you to some local places for food if you like. Additionally the train connection makes it easy to go to KL or Penang. 
 
It´s interesting to hear once about the history of the valley and its long human history once and I like it because it´s off the normal western tourist path to visit this place, however it´s not a fascinating side and rather difficult to visit.