There are lots.
Hidden Tower, Jelly World and The almost abandoned attic. Get the links to access to these places at either:
thedailyneopets.com
jellyneo.net
sunnyneo.com
yes actually there's jelly world. to get to jelly world on neopets.com you have to go explore.click a place and erase the name of the place you went and type in jelly instead.
There is one only. Jellyworld.
There are multiple secret smileys but SunnyNeo.com has a list of them all.
no only by cheating and getting banned
HEY!!!!!!!! That's a secret! *shifty eyes*
To get to Gravity mode, type in superextrahypergravitymode right after the game has loaded, on the menu screen.
You get it as a very rare zap from the Secret Lab Ray.
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well there is a lot but the only one ive been to is jelly world
There are multiple secret smileys but SunnyNeo.com has a list of them all.
The Secret of Treasure Island.
no only by cheating and getting banned
The Secret of Treasure Island
go to jellyneo.net and they have cheats for getting avatars.
Spine world Secret Builders Super Secret neopets
you can't cuddle a neopets pet! and webkinz ( found in the right places) cost less.
There are various secret avatars; about 350. All of them can be obtained in their own special way.Here are some good sites:www.sunnyneo.comwww.avatar.starried.net
you have to collect all 9 pieces of the secret laboratory map pieces
If you go into your neoboard preferences you have the option to change your avatar.