Yes, the bottom comes off. It is sealed air-tight, or is supposed to be, which is why it is difficult to remove. Remove the bolts, but not the spikes, then you can use the spikes for leverage to pull the bottom off.
The chamber for the top woofer, the hatch is behind the midrange/tweeter pod. After you remover the midrange/tweeter pod, you can't miss it.
Unbolt, but do not remove, the force-canceling bar between the woofers. There is a big foam cylinder around it, and that is glued to a crossbrace. Leaving that all intact will make reassembly much easier. You will need a socket extension to get the top bolt out.
After the force-canceling rod is loose, you will find that the woofer mounting nuts are much easier to remove. It is actually the tension of the force-canceling rod that seals the woofers in place, so don't crank down too hard on the woofer mounting nuts when reassembling.
The crossover does not have to be removed for any of this, it is in the ported chamber.