I do believe that there are infinitely more things in the world and in the universe than we can ever concieve of.
As you said, we only have 5 senses to percieve things, and even this 5 senses are pretty limited. Our vision is only able to percieve a very narrow range of the electromagnetic spectra which we call the "visible light", while the great majority of it (radio/tv waves, microwaves, infrared, ultraviolet, X-rays, gamma rays, etc) is invisible to us.
Our hearing only reaches a narrow range of sounds too (from 20-15000Hz), and there is a larger part of sounds that arent heard by us, like the ultra-sounds (that can be heard by dogs or bats) and the infra-sounds (emmited by whales for example)... and the same limitations goes for our other senses too.
So, even if we were able only to use this same senses, but alter their range of functioning, it would already enable us to percieve a lot of things we dont usually percieve.

Also, we humans have a lot of senses we arent even aware of. Many people can percieve things from other planes (which could also be called "dimensions") than the physical plane we usually live in, and so they do things like clairvoyance, clariaudience and such... what is nothing more than percieving things from other planes which are usually not percieved by our usual senses.

Our mind and brain are far more powerful and has far more capabilities than we ever imagine... we are born with them all, but during the process of socialization we all have to pass through, some of this capabilities are very used, and thus become working (like speech, using the 5 senses, rational thought, etc), and some are very little used and become dormant or even atrophied (like clairvoyant abilities for example).
And this process of selecting some brain/mind abilities to be emphatized and some to be disregarded is VERY dependent of the culture one is raised in, as people from some tribes from places like some pacific or indic islands (dont remember exactly where) can usually see and interact with what we could call "spirits" and which are completly un-percievable by us from the ocidental civilization (at least when we are in our usual state of consciousness).

There are two very good books that deals with this subjects, and i recommend them, as they are very interesting:

States of Consciousness
Beyond the Physical - Science and Occultism

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