The Metallic Lab is a track that changes every 5 waves. All the towers in the changing area will be sold when the track changes at full money back.
The first option, when the game starts.
The second option, an island with a big tree.
The third option, a magma track. You can place buccaners in magma. Black places are little coal islands.
The final option, a Temple in ruins. Bloons pass in the red path. You can repair the Temple ( will be asked ) for 150 000$.