The Lara's Shadow Add-on for Tomb Raider: Underworld has 7 achievements worth 125 gamerscore.
Find all Treasures in Lara's Shadow
Find the Hidden Relic in Lara's Shadow
Find the Hidden Relic and all Treasures in Lara's Shadow
Complete the Lara's Shadow Mission
Complete a timed speed run from the first slope in the Refinery to the back platform without saving
After destroying the Transformer, beat a timed speed run through the unstable passage without saving
Complete the combat tutorial in Lara's Shadow