In R-Type Dimensions, there are 5 hidden "spores", which resemble individual webbing, and will require a Force unit to obtain. Once a spore has been found and destroyed, it will remain so in subsequent fly-throughs.
In the Sega Master system version, there is a hidden level, the "Super Stage", which is accessed through a "hole" in the ceiling. It is full of enemies not mentioned in the instruction manual (except for Pow units). Completing this level takes the player onwards to The Den, getting destroyed returns the player to the closest Frontline Base checkpoint.
It should be noted that in the Sega Master System version, "Frontline Base" is the name for the FIRST level, this one is referred to by its defining characteristic, "The Terrible Mechanical Cells" (the Bydo Webbing, in other words)
After beating the Boss in the base you must survive for 30 seconds (since you can't fire your weapons during the ambush).This video will show how you survive the ambush. https://www.youtube.com/watch?v=uMpG0MBGUE4