Thadlerian,
The events at the Tower of Joy come from Ned's dreams and memories about the end of Robert's Rebellion. Rhaegar died on the Trident, but he'd stashed Lyanna in Dorne at the Tower of Joy. She was guarded by three Kingsguard... Arthur Dayne (the greatest knight in the realm), Gerold Hightower (Lord Commander of the Kingsguard, iirc) and one other. Well, Ned and Robert had a falling out over the sack of King's Landing (soon after the battle on the Trident) and Ned led forces south to deal with the Targaryen loyalists in the south while Robert presumably stayed in King's Landing to organize the new government (with Jon Arryn tutoring him). First Ned relieved Stannis at Storm's End and received the Tyrell's surrender. Then Ned went to find Lyanna. In the final fight, Ned took six of his companions to the Tower of Joy to fight the three Kingsguard. Of the ten men in the combat, only Ned and his close friend, Howland Reed (Meera's and Jojen's father), walked away. Ned found Lyanna lying in a bed soaked in blood (and possibly covered with blue roses)... and Ned promised Lyanna something (this is a topic of much speculation). When Ned turned to back north with Lyanna's body, Ashara Dayne (Arthur's sister and Ned's former love interest before he married Catelyn), killed herself... either from grief for her brother, despair that her love would never come back, or something else.