This Achievement is for opening all 58 Katz Chests. There is one in every location except 2. You can view all the locations in your world map. It is best to farm up your souls and unlock them before leaving the area as there really is no fast way to find which one you are missing aside from going to the world map and opening the mini map for each location to see if there is an open Katz chest on the map.
The two locations WITHOUT Katz chests are Earthpulses and Katz Corner. Every other location has one chest. Areas marked as Optional are locations that the Main quest will not take you.
The Locations are as Follows:
1) Figahl Ice Caps - This is the one that is opened per the main story
2) Hellewas
3) Beardsley
4) Hadlow Hollow
5) West Laban Tunnels
6) Vortigern
7) Port Zekson
8) Danann Highway
9) Loegres
10) Galles Lake Road
11) Barona Catacombs
12) Loegres Villa
13) The Empyrean Throne
14) Yvolg Ruins
15) Brigid Ravine
16) Vester Tunnels
17) Port Cadnix
18) Reneed
19) Fens of Nog
20) Warg Forest
21) Burnack Plateau
22) Lothringen
23) East Laban Tunnels (Optional Location)
24) Yseult
25) Maclir Beach
26) Haria
27) Manann Reef
28) Palamides Temple
29) Aldina Plains
30) Stonebury
31) Davahl Forest (Optional Location)
32) Titania
33) Taliesin
34) Perniya Cliffside Path
35) Morgana Woods
36) Aball
37)Tranquil Woods
38) Faldies Ruins
39) Lionel Island Warf
40) Baird Marsh
41) Meirchio
42) Gaiburk Ice Field
43) Mount Killaraus
44) Innominat
45) Zamahl Grotto (Optional Location)
46) Class 4 Administrative Zone - Aberrant Quarter
47) Class 4 Administrative Zone - Beast Quarter
48) Class 4 Administrative Zone - Crustacean Quarter
49) Class 4 Administrative Zone - Winged Quarter
50) Class 4 Administrative Zone - Apodous Quarter
51) Class 4 Administrative Zone - Demihuman Quarter
52) Class 4 Administrative Zone - Undead Quarter
53) Class 4 Administrative Zone - Fiend Quarter
54) Class 4 Administrative Zone - Armored Quarter
55) Class 4 Administrative Zone - Elite Quarter
56) Hexen Isle
57) Normin Island
58) Heavenly Steppes