http://uwb25d43nnzerbozmtviwn7unn7ku226tpsjyhy5n4st5cf3d4mtflqd.onion/posts/tails/index.html
If not, sometimes the site will list the .onion address somewhere on its page. To find out the addresses of sites that are only available as .onion, you will need to either find them by word of mouth, or through websites that list other .onion sites, such as this GitHub page .