Garden Folly

In architecture, a folly is a building constructed primarily for decoration, but either suggesting by its appearance some other purpose, or merely so extravagant that it transcends the normal range of garden ornaments or other class of building to which it belongs... Many follies, particularly during famine, such as the Irish potato famine, were built as a form of poor relief, to provide employment for peasants and unemployed artisans. (Wiki-Folly)

The ultimate Garden Folly.

I'm sure you know where I'm going with this: I want one! I could make one! Could I? Let's see, I would need some bricks and cement and... maybe a masters degree in landscape architecture.

I want a Master's in Landscape Architecture...

... but I'm sure I could read this book instead.

General properties of a folly according to the Wiki link above.
The concept of the folly is highly ambiguous and it has been suggested that the definition of a folly "lies in the eyes of the beholder". At best, some general guidelines can be produced, all of which have exceptions.

• They have no purpose other than as an ornament. Often they have some of the appearance of a building constructed for a particular purpose, but this appearance is a sham.
• They are buildings, or parts of buildings. Thus they are distinguished from other garden ornaments such as sculpture.
• They are purpose-built. Follies are deliberately built as ornaments.
• They are often eccentric in design or construction. This is not strictly necessary; however, it is common for these structures to call attention to themselves through unusual details or form.
• There is often an element of fakery in their construction. The canonical example of this is the sham ruin: a folly which pretends to be the remains of an old building but which was in fact constructed in that state.
• They were built or commissioned for pleasure.

What follies are not (according to Wiki)

• Follies often look like real, usable buildings, but never are; novelty buildings are usable, but have fantastic shapes. 

• Eccentric structures may resemble follies, but the mere presence of eccentricity is not proof that a building is a folly. Many mansions and castles are quite eccentric, but being purpose-built to be used as residences, they are not properly follies.

• Some structures are popularly referred to as "follies" because they failed to fulfill their intended use. Their design and construction may be foolish, but in the architectural sense, they are not follies.

• Visionary art structures frequently blur the line between artwork and folly, if only because it is rather often hard to tell what intent the artist had. The word "folly" carries the connotation that there is something frivolous about the builder's intent. Some works are considered as follies because they are in the form of useful buildings, but are plainly constructions of extreme and intentional impracticality.

• Amusement parks, fairgrounds, and expositions often have fantastical buildings and structures. Some of these are follies, and some are not; the distinction, again, comes in their usage. Shops, restaurants, and other amusements are often housed in strikingly odd and eccentric structures, but these are not follies.

So, a Masters degree... let me get back to you on that one.