Monster Arena

"''The slowly acting poison will be given to the favourite one

The dark horse will bring glory to the jailor and his men

It's always much more sporting when there's families in the pit

And the madness of the crowd is in an epileptic fit

In The Coliseum

In The Coliseum

In The Coliseum tonight.''"

- Tom Waits, "In The Coliseum"

Arena, often in the first or second big city visitable, where the party can fight slightly more advanced monsters at their leisure. To make the fights more challenging sometimes certain parameters are added to the battle requirements (beat opponent in X seconds, cannot use special commands, etc.). The game usually forces the player to try their hand at it once. In theory, many games allow you to play as many battles as you want, although some are extremely difficult until much later in the game... unless you have a Disc One Nuke.

As such an area could be prone to Level Grinding, some games do not give experience in the Monster Arena, although you might still earn items, an Evolving Attack, or a Limit Break this way. It also regularily houses a game's Bonus Boss. Of course, some games include it specifically as a place to level grind.

Sometimes this is taken in a completely different direction - the monster arena is actually an "arena for monsters"; in other words, your party doesn't fight in there - instead, a group of monsters allied to you does the fighting. Whether or not you have direct control over them varies with the game.

A popular area for the Inevitable Tournament.

Action Adventure

 * The Large Cavern in Castlevania: Order of Ecclesia. Do not enter without Volaticus and a large stock of Super Potions.

Action Game

 * Devil May Cry 2, Devil May Cry 3: Special Edition and Devil May Cry 4 have a feature known as "Bloody Palace" where one can choose to go up different levels of difficulty, facing hordes of common demons with bosses at regular intervals.
 * There was an arena in most towns in Bomberman Tournament for fighting your Pokémon rip-offs against random opponents.

Beat'Em Up

 * Appears in God Hand, which has the "Fighting Arena", containing optional difficult fights for a one-time reward, with more fights unlocking as you proceed in the story.
 * Guardian Heroes has one of these accessible early on in the game, with incredibly strong foes within.

First-Person Shooter

 * Borderlands had one of these as its second DLC.

MMORPGs

 * The Colosseum in Final Fantasy XI is one of the second type of arena; you create pet monsters to fight it out in a process involving soul-draining cameras.
 * World of Warcraft has the Argent Coliseum, a Player Versus Environment dungeon set up like an arena tournament. It houses both a 5-man and a raid instance.
 * There are also several quest chains in which a party faces a sequence of strong monsters in an arena, as well as an arena segment in Blackrock Depths that pits you against one of several possible bosses.

Platform Game

 * There are a number of Monster Arenas in the Kirby series of games, notably the Boss Rush from Kirby Super Star.
 * The Ratchet and Clank series is full of these.

Role Playing Game

 * Final Fantasy VI lets you gamble items in the colisseum. This involves having one of you characters fighting a monster while acting randomly. Have fun.
 * Fun, indeed. With a little equipment magic, and some... creative battle techniques, that place is the ultimate Game Breaker.
 * It's the norm for each Tales (series) game to have one of these, and it's generally where you'll encounter the cameo characters from previous Tales games.
 * The Colosseum from Tales of Symphonia had individual challenges (where you took on the enemies with one character) and party matches (with only three members). Most characters' best weapons and armour were earned in the Colosseum, though there they all still each get an Infinity+1 Sword from the Bonus Boss.
 * The Dragon Quest series features literal Monster Arenas; that is, ones where only monsters fight. In the early games, you just bet tokens on which monster you think will win a battle. Dragon Quest VIII re-introduces the ability to recruit monsters, so you can have a team of your own monsters fight through tournaments against teams lead by other characters, even unlocking the ability to summon your monster team for a few turns in any battle.
 * Aptly enough, the Imperial Arena from The Elder Scrolls IV: Oblivion. However, you fight sentient opponents until you reach the rank of Grand Champion, when it becomes an actual Monster Arena by pitting you against creatures of your choice, justified because the fact that you're Grand Champion makes you the best fighter in the arena if not all of Cyrodiil and no other combatants can compete with you yet.
 * Battle Square from Final Fantasy VII made you fight alone without healing between battles.
 * The Imperial Arena in Jade Empire, it also had the Bonus Boss at the end.
 * Solomon's trials in Shadow Hearts: Covenant and Lovecraft's pit fights in Shadow Hearts: From the New World offer some of the best items in the games as prizes.
 * Colosseums in Fire Emblem apparently only open their doors when there is a skirmish going on outside, as there is no way to use them between battles.
 * While these colosseums did not exist in Fire Emblem: Path of Radiance, it is revealed in that game that King Ashnard determined the ranks of his army based on who could survive a fight against a feral Laguz, making it a better example of a Monster Arena.
 * The aptly named Monster Arena in Final Fantasy X.
 * The Hades Colosseum and Olympus Colosseum from Kingdom Hearts.
 * The Olympus Colosseum was entirely composed of this in the first Kingdom Hearts. It wasn't until Kingdom Hearts II (or Chain of Memories if you want to be picky) that it became a full-fledged world.
 * Birth By Sleep also has the Mirage Arena, which is available from early in the game (it also has the obligatory Olympus visit, but all the tournaments are at Mirage).
 * Paper Mario the Thousand Year Door had the Glitz Pit, a wrestling ring.
 * Though separate from the main game, both Golden Sun games featured a Battle Mode, which players could theoretically pit three members of their party against those of a linked player or, more commonly, engage in sequential battle against random selections of every monster that save file had encountered during the game. Including bosses. You could stop between any battle, however only your longest streak of wins is recorded.
 * Chrono Cross also has the "arena for monsters" version.
 * It also had the 'normal' version at the Bend of Time
 * Arenas appear in Wild ARMs and its remake, Alter Code F, and in Wild Arms 3.
 * The Arena from Fable and The Crucible from Fable II. Both of which are part of the main plot.
 * Fable 2 also has The Colosseum, an optional quest where the player has to kill as many progressively harder monsters as they can within a time limit.
 * Dungeon Siege II has an arena hidden below Aman'lu inn.
 * Neverwinter Nights 2: Mask of the Betrayer has golem arena (arena for monsters type), which you construct golem to fight using various parts you collected from places in the game. The final battle gives you the option of betting for the proprietors soul
 * Features prominately in Mount and Blade. Every city has one, and it is a place to et experience and money. Every enemy, there, however, is human.
 * Pokémon seems to love these. There's the Battle Towers in Crystal, Ruby and Sapphire, and Diamond and Pearl; the Battle Frontiers in Emerald, Platinum, and HeartGold and SoulSilver, the Battle Subway in BlackAndWhite and of course the Colosseums in Colosseum and Gale of Darkness. Out of these, only the Colosseums reward experience, though other rewards are given in the other facilities.
 * Why wouldn't Pokémon be all over this? Pretty much the entire gameplay of the main-series RPGs is this trope but with more varied settings.
 * MARDEK 2 has the optional (and somewhat hard to enter) Trilobyte Arena, which ends with the Quirky Miniboss Squad making a return.
 * The third chapter has another one, along with shorter ones for each one of your party members.

Tabletop Games

 * At the start of Dark Sun: Shattered Lands, your party is comprised of gladiator slaves, periodically forced to fight in a colosseum. You're soon given a way to escape, but the game allows you to grind in the colosseum as long as you want for gold and xp, first. Of course, it soon encourages you to get on with the story, by releasing overpowered monsters because, since most gladiators don't survive that long, you're clearly awesome enough to handle them.

Turn-Based Strategy

 * The entire premise of Gladius.
 * While it's not an arena per se, the Item World in Disgaea probably qualifies. In addition to being one of the best level grinding spots, it's also the source of some of the game's best items and the only place you'll find teal geo panels.