Castlevania: Symphony of the Night is full of rewarding secrets to discover so here's a list of my personal favourite ones.
Keep in mind, glitches and other shenanigans won't be included here. Also, when you're done perusing this list, check out my Top 10 Useless Castlevania Secrets for a few bonus Castlevania: Symphony of the Night secrets that aren't featured here!
A tricky snack
I'm sure you picked up some peanuts along your castle-trotting quest and probably even used a few only to see Alucard toss them in the air. However, you can actually eat them by positioning Alucard under the tossed snack and holding up. That should come in handy!
Outsmarting knights is easy
This one is obvious but it makes me laugh every time. In the Underground Caverns, you'll notice a horde of Knights who seem super-annoying to get past as they're strategically placed below a tight space just waiting to jab up at you with their spears. However, if you merely push the wooden box to the right of them into the leaking water spout, their area will fill with water and they'll panic then drown moments later. Admittedly, it makes me feel kind of mean but they were trying to kill me so enjoy the drink, suckers!
Final Stage: Bloodlines rewards
In the prologue Final Stage: Bloodlines, you control Richter in his battle against Dracula. Depending on how you do in this fight, you can acquire stat boosts and bonus items for Alucard. If you completely run out of hearts, he gets a Heart Refresh while collecting extra hearts will grant him a Neutron Bomb and a Potion will unlock if you beat the boss after Maria makes Richter invincible. Meanwhile, Alucard will receive an initial stat boost if you win this battle without Maria assisting and I heard that the stat increase will be greater if you win quickly, avoid using sub-weapons, and don't get hit. Either way, doing well against Dracula will certainly pay off, that's for sure.
Early access elevator
After reaching the Outer Wall area, you'll see a wall that only mist can pass through as well as loads of Medusa heads that can turn you to stone. So, you may be delighted to know that you can bypass that barrier by going to the room above behind the Armor Lord, breaking the lower-left-hand wall, and then standing and waiting in the empty space. Eventually, a magic elevator will take you to the room below where you can acquire the awesome Jewel Knuckles and Mirror Cuirass which makes Alucard immune to Stone!
Cut #1 contains computer data
Certain versions of Castlevania: Symphony of the Night can be placed in a CD player and once you do, you'll notice that it features 2 tracks. Upon playing track 2, you'll hear Alucard say, "As you can see, this is a PlayStation black disc. Cut number 1 contains computer data so please, don't play it. But, you probably won't listen to me anyway, will you?" then a pretty cool Castlevania dance song will play that isn't featured in the game. If that's not a worthwhile secret, I don't know what is.
A buffet fit for a dhampir
It could be argued that this isn't necessarily a secret but it's something that I enjoy doing immensely. Basically, once you beat the game then purchase the Duplicator, equip it as well as a Meal Ticket in each hand. Then, you can mash both attack buttons to spawn an infinite amount of food items that get added to your inventory when collected so you can easily obtain 99 of each food type!
Alucart gets lucky
The shifty Alucart gear is seemingly the worst equipment in the entire game. However, if you equip the whole set (Alucart Sword, Alucart Shield, and Alucart Mail), Alucard's status and name change to "Alucart" and his luck stat gets a +30 boost! That should help with tracking down a few of those hard-to-get item drops. While you're at it, don't forget to equip a Ring of Arcana and Lapis Lazuli.
Fairy sings a song
If you're in the west, this will only work with the version of Symphony of the Night included in The Dracula X Chronicles or Castlevania Requiem as you'll be able to acquire the Fairy (not Faerie) Familiar. Anyway, level the little lady up to level 7 then sit in a chair, wait, and she'll eventually sing a lovely song titled "Nocturne". If you simply want to hear the song then watch the attached video below.
Sword Familiar grows up
I love the Sword Familiar. Not only does it cut through enemies and have a cool voice, it actually matures as you level it up. Once it reaches level 50, you can actually use it as a sword and it's impressively powerful. Not only that, it changes appearance as a Familiar and it looks badass. Once you level it up further, it changes a few more times and becomes quite a force to be reckoned with.
Master Librarian gets a lift
I'm sure everyone knows this secret by now but it's so much fun that it deserves top spot. Basically, work your way to the room below the Master Librarian then use the Gravity Boots underneath him to send him flying into the air. If that's not cool enough, you'll earn some incredible items after repeatedly doing it including a Life Max Up, Dracula Tunic, Axe Lord Armor, and Ring of Arcana.