Joaquin Treasure Chamber can be accessed by giving 1 Diamond Coupon to Ivan Popovichi at Thueringen Lakeside (E4). You will be warped into a room with lots of Treasure Maidens where you can kill and loot for 3 minutes. The first room contains a warp portal to the 2nd room, which in turn contains a warp portal to the 3rd room. Each use of the warp portal requires 1 additional Diamond Coupon. This is essentially a higher version of Tetra Treasure Chamber and Al Quelt Moreza Treasure Chamber.
The Lv.80 monsters in the 1st room drop Pure Talt, Pure Ionium, and Lv.80 equipment.
The Lv.90 monsters in the 2nd room drop Pure Talt, Pure Ionium, Pure Quartz, Pure Aidanium, Bellem's Box, and Lv.80-84 equipment.
The Lv.100 monsters in the 3rd room drop Pure Talt, Pure Ionium, Pure Quartz, Pure Aidanium, Pure Etretanium, Bellem's Box, Diamond Coupon, and Lv.80-84 equipment (rarely, Woodwork Hammer and Wooden Controller).