be | remain
These sites remain largely unknown to the British public.

absolutely, completely, entirely, quite, totally, utterly
His whereabouts were quite unknown during this period.

almost, practically, virtually
This drug was practically unknown in Britain.

largely | comparatively, relatively
She was then still comparatively unknown.

as yet, currently, still | hitherto, previously
a period of democratic development previously unknown in their country

apparently | otherwise
He cites the works of two otherwise unknown authors, the originals of these works having been lost.

to
Gold was totally unknown to their civilization.

great
What the weather will be like on the day is, as always, the great unknown.

into the ~
Motherhood was for her a journey into the unknown.

fear of the unknown

complete
The championship was won by a complete unknown.

virtual
a cast of virtual unknowns