Here's a good guide to successfully navigating the 6 lairs should you need help.
http://www.gamesradar.com/f/assassins-creed-brotherhood-sons-of-romulus-lairs-guide/a-20101117142249433003/p-2 (http://www.gamesradar.com/f/assassins-creed-brotherhood-sons-of-romulus-lairs-guide/a-20101117142249433003/p-2)
Here's a link to the thread (http://www.openworldgames.org/owg/forums/index.php?topic=1956.0) that contains the walk through videos of all of the lair missions