The famous Roswell event. In 1947 (some people say) a UFO crashed in Chaves County/New Mexico. And there were several (dead) aliens on board which were examined by military forces . . .  

Look for Roswell via search engines  --  try: "Roswell".

Area 51 (Groom Lake). Legendary US research facility.

Look for it via search engines  --  try: "Area 51", "Groom Lake".

The Cydonia region of planet Mars shows "monuments" which seem to be of unnatural origin  --  or not?

Look for it via search engines  --  try: "Cydonia", "face of mars". 

The Circles Effect  --  almost forgotten. But they are still there!

Look for it via search engines  --  try: "Kornkreis(e)", "Circles Effect".

HAARP (High Frequency Active Auroral Research Program)  --  a top secret research project by military forces.

The technology is based on N. Tesla's studies on electricity. Very strange research without any detailed official statement.

A book dealing with HAARP states: "Angels, doen't play that harp."

Look for it via search engines  --  try: "Tesla", "HAARP".

Crystal Skulls  –  presumably manufactured by human beings hundreds or even thousands of years ago: nobody knows how it was done. The mediums are rock quartz crystal, amethyst, topaz, citrine, and others. 49 of these skulls are known; one of it (first two photos on the left) can bee seen at the British Museum/London.

Look for them via search engines  --  try: "Crystal Skull(s)".

Everything you want to know about them can be found here: skepdic

Coral Castle  –  a "historical site" in Florida. In 1920 the Latvian Ed Leedskalnin began to build a castle out of hundreds of coral rocks. Weighing up to 1,000 tons nobody knows how he managed it to put the rocks to their locations. After 30 years of building his castle Ed died in 1951. Some people say that he was able to let the rocks hover to their places.

Look for it via search engines  --  try: "Coral Castle", "Leedskalnin".

An extensive overview of unnatural and metaphysical related subjects can be found here: Ellie.