SE of Page 2 miles from the junction of Coppermine Rd and AZ 98
You can get a photographer's permit which lets you in for 2 hours. When I went there were very few people so I could stay as long as I wanted. Upper Antelope is the more popular and even with a photographer group you are rushed through.
This photo was taken in Lower Antelope Canyon. Reflected light on sandstone is beautiful. Here both sunlight and sky are reflected.