Gandalf falls at Bridge at Khazad-Dum
"In the Halls of Moria" by Alan Lee
On the first night in Khazad-dum Pippin drops the rock into the well. After a hope inspiring pause, out of the depths the company hears: tap-tom, tom-tap.... tap-tom, tom-tap, tap-tap, tom. The fellowship passes a tense night but nothing further happens on that night or for the next 2 days.
After two marches the company reaches the room where they find Balins tomb and the hope that Gimli carried dies. They read the account of what happened in the room and while they are there they are attacked by orcs. The company manages to escape but not before Frodo takes a memorable blow from an orc javelin, which he miraculously survives. But, during the struggle, Gandalf is drained fighting some unknown evil while defending the doors.
The Company runs for the bridge; hope of escape is in sight. The orcs are far away and separated from the crew by a chasm. It looks like the company is going to make it across Durin's bridge and then Legolas and Gandalf see that nameless evil - a Balrog. Even weakend he is able to send the Balrog to the depths but Gandalf falls with it.