This level occupies the map slot MAP16. For other maps which occupy this slot, see Category:MAP16.
Opening the blue skull key room from outside (assumed you came through the hallway), you just crossed a triggerline that opened (a room behind you and) the bars that blocked the cave entrance in the very north of the eastern map part. Enter that cave (sector 175) to get a soul sphere.
Enter the teleporter in the south of the cave east of the big bright arrow pointing at the yellow skull key. Exit the destination teleporter to register this secret (sector 289) and find a blue armor.
Still in secret #2, simply grab the blue armor. It is located on the adjacent but also secret sector (sector 404).