[[caption-width-right:320:One day, I'll be rich enough to afford the cure for my decolorizing skin condition!]]
A 1991 side-scrolling PlatformGame (or rather, a series thereof) by Apogee Software (now 3D Realms), ''Crystal Caves'' features the unlucky space trader Mylo Steamwitz as he searches mines of the Altairian system for crystals [[ExcusePlot so that he can invest into several get-rich-quick schemes]]. On his way, of course, he runs into countless monsters, hazards, locked doors, power-ups and other standard platforming fare. The goal on each level is to collect all the crystals and get to the exit.

The game was actually released as three separate episodes, each one featuring new levels and some minor changes in graphics. The first one was [[{{Shareware}} made available for free as a teaser]], while the next two were available for purchase. The game is still sold on the 3D Realms website. It uses the same engine as SecretAgent.

Not to be confused with ''VideoGame/CrystalCastles''.
!!This game provides examples of:
* AlliterativeTitle
* ArtisticLicensePhysics:
** Some levels have "low gravity". This does not mean that you fall more slowly or that you can jump higher. Instead, shooting your pistol causes you to recoil backwards. When standing on the ground, the difference between normal and low gravity could be explained by noting that the amount of friction is proportional to your weight. However, the same difference occurs in midair.
** Some levels have inverse gravity, which means you fall ''up''. Others have a timed pickup that reverse gravity temporarily.
* AttackablePickup: Some of the levels have five eggs scattered throughout. Shooting an egg instead of picking it up turns it into a letter. If all five letters are collected, the player receives a large score bonus. (The uncracked eggs are worth 1000 points each, while the individual letters are just 100 points each without the bonus for all five.)
* {{BFG}}: Your pistol fires ''rockets''.
* BlackoutBasement: Several levels in the series are like this, though they tend to come with a light-switch somewhere. One of them has inverted gravity to confuse you even more.
* CollisionDamage: All the enemies, as usual in platformers. Two enemies leave behind corpses that harm you on touch.
* DrugsAreBad: The shareware episode has a sign reading "Winners Don't Do Drugs" on the overworld map.
* ExplosiveDecompression: There is one air generator on each level; if you shoot it, the vacuum rushes in and Mylo immediately explodes.
* FloatingPlatforms: Which can be switched on and off.
* ForcedTutorial: The text boxes which appear every time you come upon something new. Even if you just restored an old game!
* GetRichQuickScheme: Mylo's motivation in all three games. He's apparently famous enough for falling for these that this earned him an entry in the Galactic Encyclopedia.
* GoForTheEye: There is one baddie that you have to shoot each of its syes twice (when they're open), then its body three times to defeat it.
* GravityScrew: Some levels have low gravity, a couple have reversed gravity, and some levels include a timed pickup for temporary reversed gravity. The GodMode cheat code also allows you to reverse gravity whenever you want.
* GuerrillaBoulders: Some levels have the sign "Falling Rocks"--guess what keeps happening there?
* HeartsAreHealth: Your LifeMeter is made out of these.
* InexplicableTreasureChests: Scattered around, can be opened for score if you find a key.
* InvincibilityPowerUp: The very rare red mushroom.
* InvisibleBlock: As usual, they show up when you bump them from below.
* JumpPhysics: You always jump a fixed distance, and can steer freely in mid-air.
* LevelGoal: Represented by rather complex-looking, big mechanical doors.
* LockedDoor: Each level has one which is unlocked by collecting all the crystals in said level. Some levels have additional locked doors which must be opened with keys before the final door can be unlocked.
* NoDamageRun: You get a reward after finishing a level if you pull it off.
* PoisonMushroom: The green mushroom kills you instantly when you touch it.
* SegmentedSerpent: A green snake-like enemy.
* {{Shareware}}: As with many other DOS games of the time, the first episode is free as a teaser.
* ShoutOut:
** Some levels have falling crates with the text "ACME" on them. This refers to Acme Corporation (and especially their anvils) in ''[[WesternAnimation/{{LooneyTunes}} Looney Tunes]]''.
** One level has a sign which reads "[[{{KilroyWasHere}} Kilroy was here.]]"
** The sign with the text "Winners don't use drugs." is a reference to a slogan which appears in some arcade games in the U.S.
** One level in Episode I has green mounds that look suspiciously like the green mounds from Super Mario Bros. 2, and a pipe at the top of the level, complete with a mushroom on it, resembles the classic warp pipes from Super Mario Bros.
* SideView
* SpellingBonus: The letters in the eggs (see AttackablePickup above).
* StalactiteSpite: Some of the stalactites fall with a loud sound effect as you pass underneath.
* TreasureIsBiggerInFiction: The crystals are the size of Mylo. How can he carry tens of them is anyone's guess.
* UndergroundLevel: All of them!
* UnwinnableByDesign: Some levels require pre-planning or trial and error to get through without getting stuck. This especially applies to levels with the gravity reversing, invincibility, or gun upgrade powerups, all of which last for a limited duration. Thankfully, you can retry any number of times.
* UnwinnableByMistake: In the third episode, two of the levels in the HubLevel are located in an area that you can't jump out of. If you drop down into the area before completing all the other levels, you're stuck. Thankfully, it is possible to leave via cheat codes.
* WallMaster: A purple reptile (it also has a cameo on the title screen).