Wondermine

"You never know what treasure a Monster might find in the Wondermine. Everyone should have a turn! Monsters with multiple elements can find better things in here. They'll be away for a while, but it's worth the wait."

The Wondermine is a primary production structure in Dawn of Fire. Uniquely amongst the other production structures, the Wondermine does not simply produce items from nothing - instead, a monster which is residing on the Continent must be sent into the mine to find them. Monsters of any level may enter the Wondermine, and any monster sent into the mine is temporarily removed from the Continent, with its position being marked by a signpost. While in the mine, the monster does not sing, and cannot be fed, sold, moved or teleported to another island, though it may be used in the Breeding Structure. The monster's level and species appear to have no effect on the items which may be found in the Wondermine, only the number of elements. Monsters on the Outer Islands may not be sent into the Wondermine.

The Wondermine is not purchased from the shop, but is instead found already-built on the Continent, in the Cold Lands directly above the Castle. It may be accessed when the Cold Lands is unlocked at level 9.

Produce
On each visit to the Wondermine, your monster will also bring back some other object. These appear to be randomly chosen from all of the items that you would be able to get from your primary production Structures (the Fruit Tree, the Garden Patch, etc.), as well as Apple Tarts. As you reach higher levels and your structures are able to produce more kinds of items, the variety of items you can get from the Wondermine increases.

Strategy
Compared with a single-element monster, with each additional element, the monster spends double the amount of time in the mine, and has double the chance of bringing back each item... to a maximum of 100%, of course.

As a statistical average, there is no difference between sending a single-element monster twice and sending a double-element monster once. But if you consider the statistics without averaging, sending the single-element monster twice has some chance of bringing back two of each object, but a reduced chance of bringing back just one. Also, with each trip to the mine, a monster brings back one additional item apart from the special items (slime, mushrooms, amber, etc.). Sending a monster twice will give you two of these random items instead of just one.

When you get up to the three- and four-element monsters, the probability limit of 100% affects the statistics for slime, mushrooms, and hot peppers. For example, the statistical average result for 4 trips of a 1-element monster or 2 trips of a 2-element monster is to give you 1.6 Slimes, while 1 trip of a 3-element monster gives you just 1 Slime. Some of the expected return is "wasted" because the probability can't go beyond 100%. On the other hand, for planning purposes, it's sometimes good to know that you are absolutely guaranteed to have one of those things, rather than just having a a good chance of 1 and a possibility of 2.

If looking for a Crafting Item where there is never a 100% guaranteed success of find one, consider using a Quad Element Monster, rather than using monsters of less elements. For the same time period, having one single trip for a Quad Element Monster is more worth than going twice with a Triple-Element Monster to get a single rare Crafting Item (for example, Amber).

And, of course, you have to be actively playing the game in order to send a monster out. If you're going to be away from the game, you might as well send a monster for as long as you're going to be unavailable, so it can explore the mine while you're busy. If you're going to be working on the game and want lots of random objects, send in 1- or 2-element monsters for lots of short trips.