Play Glacial Chasm either from your hand or from your graveyard.
When Glacial Chasm enters the battlefield, it triggers Druid Class and its own second ability.
Resolve the Druid Class trigger, gaining 1 life.
Resolve the Glacial Chasm trigger, causing you to sacrifice another land you control.
Play any land from your graveyard.
When the land enters the battlefield, Druid Class triggers, causing you to gain 1 life.
At the beginning of your next upkeep, Glacial Chasm's cumulative upkeep ability triggers, allowing you to choose not to pay the cost and sacrifice it instead.