Follow the red arrows on the screenshot pieces.
(Pictures included)
Warp to the Hidden Temple Dungeon:
(http://i148.photobucket.com/albums/s25/taderadeva/ragnarok/0.jpg)
On the first map, east:
(http://i148.photobucket.com/albums/s25/taderadeva/ragnarok/1.jpg)
Again east:
(http://i148.photobucket.com/albums/s25/taderadeva/ragnarok/2.jpg)
Now south:
(http://i148.photobucket.com/albums/s25/taderadeva/ragnarok/3.jpg)
East again:
(http://i148.photobucket.com/albums/s25/taderadeva/ragnarok/4.jpg)
Finally north:
(http://i148.photobucket.com/albums/s25/taderadeva/ragnarok/5.jpg)
Now you should be on a bigger map with a bridge in the middle of it:
(http://i148.photobucket.com/albums/s25/taderadeva/ragnarok/6.jpg)
Cross the map and you'll reach Prt_Maze03, the harder level of the Hidden Temple Dungeon. On several maps, you'll find the Bapho Jr. monsters.
http://i148.photobucket.com/albums/s25/taderadeva/ragnarok/7.jpg
Be careful! Bring a Butterfly Wing with you, you can get lost easily in there.