3. The Sperrin Mountains, counties Tyrone and Derry-Londonderry
Hear spring, think lambs. Hear Sperrin Mountains, think walking. Straddling two counties (Derry-Londonderry & Tyrone) the Sperrins are modest in size but pack a varied punch.
You're in stone circle country, here, too. According to WALK NI, "Over 90 sets of stone circles have been found in the Sperrins, the best known being Beaghmore Stone Circles in the south east of the range. Despite being relatively small in stature, the alignments of the Beaghmore Stone Circles accurately correlate to movements of sun, moon and stars."