Class trainer

When a Player's Character in DDO gains enough experience to increase a level, they must visit an appropriate trainer, i.e. a trainer of that same class as their next level. This is true whether that character is continuing with their pre-exixting class(es), or if they wish to gain a new class (multiclass).

Note that this is only true for "Heroic" levels, 1-20. After 20, the character is no longer (merely) Heroic, and must visit a Fatespinner for Epic level training.

For those spellcasters who must choose their spells as they level (namely Bards, Favored Souls, Rangers, Sorcerers and Warlocks), trainers can also swap old spells for new - for a (reasonable) price. (Other casters, namely Artificers, Wizards, Clerics, Druids and Paladins, can freely reset their spells in any Tavern, choosing from the spells they have at their selection.)

Trainers can also be used to (re-)set enhancements (at any level), but that can also be done in any public place with the keys ctl.

Trainers also allow certain classes with summoned "pets" (e.g. an Artificer's Iron Defender, or a Druid's Wolf Companion) to train those pets, purchasing enhancements with the pet's Action Points, similar to how characters can for themselves.

Korthos Village
All classes.
 * Trainers for Barbarian, Cleric, Favored Soul and Paladin are grouped just off the village square, just west of Korthos Hall.
 * Artificer, Fighter, Ranger and Sorcerer Trainers can be found between Korthos Hall and the gate to Korthos Island.
 * Bard, Druid, Monk, Rogue, Warlock, and Wizard are loosely grouped in the far west of the village, behind the Wavecrest Tavern and near the Heyton Family Crypt.

The Harbor
All classes.

There are actually 2 separate groups, duplicating trainers for all classes - one is found in the far northeast on the dock level, northwest of the Leaky Dinghy tavern, and the other in the southern walkway, scattered east of the Wayward Lobster tavern.

The Marketplace
All classes, found in the southmost area, near the gate to The Harbor (around the fountain there)

House Jorasco
Only "religious" type classes, plus Barbarian:
 * One Paladin, the Favored Soul and Barbarian trainers are in the southeastern area, near the Airship Portal. The Barbarian trainer is "hidden" up the path to the right of the gate to Delera's Graveyard.
 * One Cleric trainer is in the southeastern area, near the Open Palm Inn
 * The other Cleric and Paladin trainers are on the southern edge of the enclave, near the House of Wizardry.

Special
 * Feat re-trainer - Fred

House Deneith
All classes, in the far northwest near the Airship Portal.

House Kundarak
Only Barbarian, Fighter, Paladin and (2) Rogue trainers.
 * The Paladin and Fighter trainers are at the foot of the ziggurat in the eastern area, between the Bank and the Airship Portal.
 * The Barbarian trainer is on a small wooden platform in the western area, just west of the two bridges.
 * Both Rogue trainers are in the western area; one in the southeast off the alley to the Ever Full Flagon tavern, and the other in the northwest, around the corner (west) from the Stormreach Teleporter.

House Phiarlan
Only (classic) arcane caster trainers.
 * Bard, Sorcerer and Wizard trainers on the central dais, east of (and above) the Golden Wing Inn.
 * Another Sorcerer and Wizard trainer north of the Golden Wing Inn and a mailbox, near a fountain.

Ruins of Threnal
Note that these trainers are not exactly "convenient", unless you happen to already have fought/snuck your way through the wilds of Threnal. These trainers can all be found within the walls of the southern compound.
 * The Fighter trainer is northmost, on your left as you enter.
 * The Sorcerer trainer is in a tent southeast of him, in the eastern area of the compound beyond Sal Danek.
 * The Rogue trainer is in the central area of the compound, not far from the Southern Ruins.
 * The Cleric trainer is in the western area of the compound, against the far west wall.
 * The Barbarian trainer is south of him, down in the sunken portion of the area, near Jan Falner.

Portable Hole
Sorcerer, Warlock, and Wizard only. All 3 are found in the central hall.

Amrath

 * All classes

Eveningstar

 * All classes, in a group near the southeast edge of the village.