To start the hengestone quest, go and talk to the hengestone manager inside roboldeoux pioneering support centre. You must be level 40 to intiate the quest. You can touch them before the quest, but they will not count as found. I touched about 4-5 of them on my travels and It said I found my first one when I touched the one in Porto bello. So do not hunt for them until starting this quest.

There is/should be a hengestone on every overworld map, apart from towns & cities.

There should be a total of 50 hedgestones, because the compensation list has items for up to 50 hedgestones.

Compensation List: (Listed here for completiviness)

===10 Hengestones===

1. Magical Orb (xx)
2. Elemental Orb (50)
3. Rifle Bullets (xx)
4. Toolset box (50)
5. Enchant chip level 68 (3)
6. Level 30 EXP card (9)
7. Golden Coupon (2)

===20 Hengestones===

1. Cinquedea (1)
2. Level 40 EXP card (9)
3. Bracelet of Hellfire (1)
4. Unicorn Rod (1)
5. Brown Bess 34 (1)
6. Enchant chip level 72 (3)
7. Knightsword (1)

===30 Hengestones===

1. Violent Shooting Star Ring (1)
2. Might Staff (1)
3. Box of Bellem (10)
4. Jambiya (1)
5. Level 60 EXP card (9)
6. Enchant chip level 76 (3)
7. Studded-Leather Armor (1)

===40 Hengestones===

1. Into ###### Ring (1)
2. Mysterious Amber (10)
3. Platinum Coupon (2)
4. Rod of Darkness (1)
5. Persqabz (1)
6. Enchant chip level 80 (3)
7. Leranja e Pretol (1)

===50 Hengestones===

1. R.I.P Ring (1)
2. Mysterious amber (10)
3. Bellem's Box (10)
4. Diamond Coupon (1)
5. Albaes (1)
6. Enchant Chip level 84 (3)
7. Bracelet of Neptune (1)

Pillar locations:
Here is the list of pillars (sorted by level range) that have been found throughout the world of Granado Espada. Newly discovered hedge stones will be marked with *NEW* for a duration of 1 week. Enjoy!

1. Queen's Gate I2 At the top right most corner.
2. Stone Pit C2 Near Jack's house. [1-4]
3. Ferructio Junction H9 Hiding in the small ledge. [4-7]
4. Al Quelt Moreza H7 Near the fountain. [7-10]
5. Al Quelt Moreza Nartex D8/C8 Behind one of the pillars. [10-12]
6. Cathari Falls F9 Southwest of the bottom of the cliff. [17-19]
7. King's Garden F6 Walk down slope and turn left. [19-22]
8. Tetra Hill H9 Cave room where u can go to the other super high level area. [22-24]
9. Tetra Ruins F9 In a very small corner at the side of the ruined building. [24-26]
10. Coimbra Nimrod Bridge I3 In the nook at the side of the left stairs, time oriented: Appears at 10am(PST)/11am(PDT)10am(SST) and disappears after ~5 minutes.
    
11. Jezebel Glen H6 Near Colony Manager orb. [34-36]
12. Porto Bello G6 Near the waypoint [36-38]
13. Porto Bello Deck J6 Second to last square room. [38-41]
14. Porto Bello Deserted Quay E1 Next to the gateway to Desolate Cliff. [46-48]
15. Thueringenward G4 Inside the stone circle. [48-50]
16. Porto Bello Desolate Cliff H5 About 15m away from the nearest cliffs. [48-53]
17. El Lago de Tres Hermanas I7 Northwest edge under hill. [50-53]
18. Theuringen Lakeside D6 Across the river of the Golden Well.
19. Dr. Torsche's Mansion: Savage Garden G3 On the side of the mansion. [53-55]
20. El Tejado Verde F8 [55-60]
21. Pradera de Ceniza E3 [60-62]
22. Rion Prairie H3 [62-65]
23. Bonavista River F5 Positioned in the narrow corner. [65-67]
24. The Crater of Joaquin H7 Top of the middle crater. [65-70]
25. Lava Plateau of Joaquin F2 Right next to the waypoint [70-72]
26. Prison de Joaquin, The Mohrgus E5 In the middle of a circle. [72-74]
27. El canon de Diabolica G2, Next to cliffs. [78-85]
28. El Ruina Memoria E9 [71-78]
29. Vegas Javier F2 [65-72]
30. Ustiur Zona Uno G6/G7, Within the trees. [??-86]
31. Ustiur Zona Dos E11 [level 86 above]
32. Lago Celeste E3 [85-87]
33. Rio Alibi I7 Up the hill.[87-90]
34. Skull Dungeon level 3 C6[94~97]

Total Hengestones: 34

Note: Thanks to Soap and darkstrike of the official forums for posting the info, and thanks to the original creator ahB0i from the korean forum.