chessGMSacrifices on the h-file is lesson 1 of 7 in Sacrifices on the king, a tactics course suited to players rated around 1200 (improving players). Give up a piece on the h-file to open it: a rook or queen arriving on the open file next to the castled king is often deadly (on the a-file when the king castled long). It has 6 interactive exercises: 6 calculated lines from real positions. You play every move on a board and get feedback straight away. The lesson is free.