Err_too_many_redirects

Can somebody take a look?

http://polki.uni.lodz.pl -> ERR_TOO_MANY_REDIRECTS
but http://polki.uni.lodz.pl/polki2016/ is OK

Domain is redirected

My .htaccess
RewriteCond %{HTTP_HOST} ^(www.)?polki.uni.lodz.pl$ [NC]
RewriteCond %{REQUEST_FILENAME} !/polki2016/
RewriteRule ^(.*)$ /polki2016/$1 [L]

What exactly is your desired outcome?

I want to my website address was polki.uni.lodz.pl
I don't know what is wrong

Why don't you just install at the root of your webroot folder? Why even have it in a subfolder at all?

made up for it a couple of things,
I would like to know
if the problem is on my side
or simply Getgrav so has

Other CMS work

Pretty sure it's your side. Or your rewrite configuration at least. Grav is not doing anything special. The .htaccess for Grav is very close to Joomla or WordPress.