Hot Cold bonus level
Go to Level 14 and ride about half way through the level to 
find alien crossing sign on the left hand side. Run into 
the sign to be transported to level 31.

Eggipus Rex bonus level
Go to Level 11 and proceed until reaching the area where the 
huge dinosaur chases Crash. Allow the second pterodactyl capture 
Crash to reach level 32. 

105% completion
Collect all relics and gems, including those from the Hot Cold 
and Eggipus Rex bonus levels. Then, approach Crash's sister, 
next to the save spot, to find another clear gem. Take the gem 
to view a very nice fireworks display and finish with a 105% 
completion status.