Start by having Olaf climb the ladder, collecting the fruit on the way up. At the top, switch his shield so it's above his head, and have him glide to the bottom while avoiding the fiery areas (if a viking touches the fiery areas, he will die instantly). At the bottom, get the blue key and use it to open the door so the others can go through. It is only necessary to take Olaf and Baleog through the door; Erik can stay at the start for now. To the right of the door is a steep slope and a blue lizard. If Olaf tries to block the lizard with his shield while they are on the slope, the lizard can hurt him anyway, so just lure it down to the flat part at the bottom so Baleog can destroy it. Now Olaf should continue to the right. Ignore the ladder and keep heading right until Olaf encounters a blue-haired caveman. This enemy is very annoying because it is invulnerable while rolling, and it pushes Olaf back a little bit when it rolls against his shield. Just have Olaf block it as far to the right as possible and have Baleog keep shooting arrows at it until it dies. Remember, Baleog's attacks can only hurt the caveman when it is not rolling so time the arrows to hit it when it is vulnerable. Once the caveman is destroyed, have Olaf go back to the left and climb the ladder to get the red key. Once the red key is collected, use it to lower the bridge so Olaf and Baleog can cross the lava pool. Have Olaf go to the right and climb the ladder. If he jumps off the ladder from the top and falls down the ladderwell while moving to the left, he will pass through a false wall and collect a hidden fire arrow and piece of meat. At the top of the ladder, he and Baleog need to destroy the blue lizard near the gold keyhole.
Now it's Erik's turn. Back at the ladder where the vikings started the level, have Erik climb the tall ladder and at the top, have him jump to the right onto the platform where the steak is. He can bash the wall to the right with his head. He is vulnerable to the snail there, but remember that touching the snail directly does not hurt a viking. He can pass right through the snail without being hurt as long as he isn't hit by the snail's projectiles. It's best to ignore the snail and the ladder and have Erik proceed to the right after bashing the wall. Get the gold key, and then have him fall off the ledge to the right where the gold keyhole is. After Erik opens the door with the gold key, there is another annoying caveman to take care of (or ignore) before the vikings can climb the ladder back to where Erik smashed the wall. Take care of the remaining enemies (which should be easy if you collected the hidden fire arrow) and climb the ladders to the exit.