It might work, though there is also elo.

In•yngyl dhaer daw? 'The great spiders there'.

+Matt Dinse Doesn't elo have more of a positive connotation?

+Александр Запрягаев I cannot find taw anywhere, neither in Eldamo nor in VQP, other than slossed as "wood/wool (those two are almost the same thing, right :-P)". Also, I sort of remember ennas as "over there". 

Perhaps No tirweg! Yngyl dhaer!?

+Hjalmar Holm "Elo! Yngyl dhaer!", ebent i aew ar e avant hain. :P

There is also alae which might be neutral, like Latin ecce.
Using cen- in the imperative feels weird to me, since it's non-volitional, you can only decide to look, but not to see (apart from weird specific contexts). So tir- seems better.

I've suggested before, you can use nuia-(?) [NUS+ja] or nosta- [NUS+ta] as "to notice, perceive, sense, smell". These, in imperative form, would do just fine, in my opinion.

Nuio/Nosto in-yngyl dhaer!

Or you can use alae and nae interchangeably depending on the context, e.g.:

Alae, yngyl dhaer!, when you' re happy to see such beautiful huge spiders ('cause you're an arachnologist or a hungry bird)

Nae, yngyl dhaer!, when you're threatened or disgusted at seeing such huge hideous spiders

Btw, for taw see PE/19:104 and PE/21:58.

+Lőrinczi Gábor I found it in PE 19, but not in PE 21. 

+Hjalmar Holm " tā̆d, thither = Q tar, ON tō "