Yep, this is a rock brick. Useful for doing landscaping, or building small mountains for Lego figures to climb on. Put several of them together, and you have a whole mountain range. I used a bunch of these to build a small mountain with a waterfall cascading down into a small lake.
Here's an inside view. This piece can also be used as a nice fireplace. Stick a couple of Lego flames inside, build a chimney, and there you go.
Some of the pieces I got with the set have designs printed on them. Beware of the menacing aliens!
This piece is useful for castle building. It also comes in white, gray, and black, but I didn't have a piece of that color handy. It was used in one of my favorite Lego sets of all time, the Eldorado Fortress, a set from when I was young. Here's a picture from the inside:
Opens up some interesting new possibilities for castle building, does it not?
This is another useful brick. As its name suggests, you can use it for mounting headlights on cars, as the stud mounted perpendicular to the other stud lets you do. It can slao be used for mounting plates vertically:
And, the shape of the headlight bricks lets them be built into some interesting configurations. The photo above shows four headlight bricks, mounted at 90-degree angles to each other.
This is one of the most basic parts of the Lego building system. These plates can be found in almost any model made of Lego bricks. Their uses are simply too many for me to list here, but here's a few I thought of:
Notice the offset of the pistons in the cylinder casings. That comes from the bent crankshaft, a small part of which you can see in the above picture.
Front view of the engine. That axle in the center is connected to the crankshaft; turn the axle, the crankshaft turns, moving the pistons up and down.
Bottom view, showing the crankshaft and pistons in more detail. The red bricks are another useful type of Lego brick, which I'll talk about in a future BOTD.
