To obtain the Raval Shield, you must bring the Lotus Hammer to Adonis (the Blacksmith in Redmont town) and give him 1000 Raval Ores. This guide will show you where to find the Lotus Hammer and Raval Armor.

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Once you have access to Genos Island, go inside the dungeon (Dark Shrine) and follow the path until you reach this area:

Jumping into the square hole shown in the image above will land you on some platforms which leads to a red treasure chest containing the Raval Armor:
Below the platforms are lots of Skull-Alnadas (skeleton swordsman enemy) and a Skull-Magiste (skeleton mage enemy), both types will be immortal and not yield any loot or EXP until you obtain and equip the Silver Chime, which we getting next.

Going to the upper right exit from below the platforms will lead you to an area with 2 vertical paths, one with lots of Doonos (dragon/skull laser enemy) and the other with lots of Skull-Alnadas. Run through the path with the Skull-Alnadas to find the Silver Chime inside a red treasure chest:
With the Silver Chime equipped, you can now kill the skeleton enemies and they will drop loot (some gold and 5 to 10 Raval ore). You can either go back to the platform area by backtracking or follow the path with Doonos to get back to the area with the square hole (this path is longer, but has a brown chest with some Raval ore on the way).

After returning to the area with platforms, go south and you should see a red treasure chest in the middle of the path. Open it to obtain the Lotus Hammer.
Talk to Adonis (the Blacksmith back in town) when you have the Lotus Hammer and 1000 Raval Ore and he will craft you the Raval Shield.

If you have the every sword, shield, and armor at this point, you can upgrade them all to max to obtain the "A Talent for Forgery" achievement.

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Farming gold and Raval ore in the Dark Shrine:

Upgrading equipments can cost a lot of gold and Raval ore. You can farm the Skull enemies (swordsman and mage) for a decent amount of gold and ore; and the huge plant and huge bipedal armored-werewolf enemies further in the shrine for up to 500 gold and 10 to 25 Raval ore each enemy.

Remember to have the Silver Chime equipped if you wanna farm the Skull enemies.