Unepic

Yes, this is a grinding achievement. Rest assured you'll at least get 5k to maybe close to 8k by the time you're done with the story and any side quests. If you're level 17 (soft max level for weapons in single player), you may be close to 9k kills.

This achievement may take additional 2-3 hours of game time, in the same file, to finish depending how many you killed prior to the final boss fight from the Mage's Tower.

Here's a few suggestions:

• Skills: Any that penetrates through enemies or affects more than one in a or multiple directions. Any x3 weapon masteries (use the inner parts of the castle to max out)
• Weapon: Have either an Axe or Mace to attack skeletons in the Catacombs (they will mob and use ladders), Bow for insects (if not using range spells), Sword or Spear for most enemies.
• Spell: Any that hits multiple enemies (be sure to keep a safe distance as some spells can hit you back), Heat Aura (Level 4 Fire, for bats/crows), Improv. Healing (Level 10 Healing), Improv. Regeneration (Level 12 Healing), Antidote (Level 8 Healing), Sleep (Level 1 Mental, for tough enemies), Light if Catacombs, Teleports to each section of the castle (Level 9 Alteration or scrolls)
• Recommended Areas: East, Center, Down, West (to start) Jail, Halls, Mine (if not friends with the goblins), Sewer, Garden.
• Areas to avoid: Lab, Tower, Library (due to heavy damage range magic), Catacombs (unless you have a good blunt weapon or points in Light), Mage's Tower (not ideal for grinding).
• Recommended Pets: Plant, Gatchan, Skull (for non-undead monsters). Note: Pet kills or frozen by Coldax do not count.

As for what paths to take, start in the inner areas (gray on the map) then branch out in either of the recommended areas. The monsters respawn after about 5 different room changes, so be sure to check back on those spots (especially the two rooms to the west of the save box, the room west, down, west of the save box, and any crow/bat filled rooms with Heat Aura).

Having music playing outside of the game may help ease the boredom, or chatting with friends if you can talk and grind at the same time.

Happy Grinding!