Here is the top bar hive from the north side, with the viewing window closed.
Here is a side view. The cord is holding the bottom board on.
Here the hive and the viewing window have been opened up. The bee entrance holes can be seen on the far side. The bee space is the lighted section, it can be expanded by moving those boards.
Here is a close up of one of the bars (upside down). The theory is that the triangular shape will encourage the bees to build the comb straight along the bar.