Turok 2: Seeds of Evil

This is missable if you don't create a separate save before entering the final boss.

On each level there are two warp portals: one is used to obtain the game's talismans, the other is a "fake" portal, filled with enemies that you must progress through. The portals can be quite difficult to complete so it is recommended you take your time and be stocked up with health and ammo before entering.

They all however have regenerating health and ammo located somewhere within them and upon completing each one you are rewarded with a piece of the nuke weapon. Although obtained very late in the game, the nuke can be handy in the final fight against the Primagen.

The locations of the portals can be found in the following.

Port of Adia

River of Souls

Death Marshes

Lair of the Blind Ones

Hive of the Mantids

Primagen's Lightship