There are two ways to get into the villa: you can either work your way around the rocks to the rear of the house, or trek through the perilous sewers. Needless to say, the first option is easiest.
Option 1
Face the doorway to orientate yourself, then follow the wall around to the left, heading down the steps. A little further along the path, the buildings fall away, revealing an impressive vista of the surrounding countryside. Look for the small wooden steps on the left and head down to the lower level. Next, locate the small ledge a little way on and drop down to the grassy path winding around the rock. Follow it forward, leap over the gap and push on through the bushes.
On the other side, drop off the next ledge and begin scaling the rocks to the right. Swipe the love letter from the body on the ground then climb the final rock to the right to enter the villa grounds.
Option 2
Face south with the villa entrance behind you, then look for the steps to the south-east. Make your way down and locate the grate immediately to the right at the bottom. Descend the ladder and follow the sewer passage to the north-east, heading in the direction of the objective marker.
Keep pushing forward, dealing with the Water Hag and Drowners that that attack as you wind along the tunnel. Eventually it comes to and end and you'll emerge outside with the countryside stretching beneath you. Look for the ledge to the left and climb on up. Swipe the love letter from the body on the ground then scale the final rock to enter the villa garden.
http://www.eurogamer.net/articles/2015-05-18-the-witcher-3-walkthrough-3696?page=16
