Some unused level data might be inside, though there are no hidden or unused levels in the data tables.
Press Select on the title screen.
The game has a total of five 4Kb full CHR data banks in the ROM. The fourth one is never used, though, and is actually an early version of the main game's CHR data bank: different starting point graphics, arrow graphics, old uncleaned route tracks, different switch points, some routes don't have graphics at all yet, etc.
If you like to see how it looks inside the game, use Game Genie code LASKAAPA.