I'm planning a summer visit to Mont-Cenis. Could you tell me the name of the free natural attraction available, which historical military fort is recommended as easy to visit, and approximately how long it takes to walk around the Mont-Cenis lake?
Navigate to the 'Mont-Cenis' page on haute-maurienne-vanoise.com. Locate the name of the free natural attraction open in summer. Identify the specific military fort mentioned as easy to visit in summer. Find the approximate walking time for touring the Mont-Cenis lake. Synthesize the names of the free natural attraction, the easy-to-visit fort, and the lake walking time.
State that the free natural attraction is the 'Jardin Alpin' (Alpine Garden). State that the fort mentioned as easy to visit in summer is the 'fort de Ronce'. State that it takes approximately 5 hours to walk around the lake.