Onboard/Offboard is a series that explores the can't-miss highlights of our favorite cruises—from the shore excursions to book to the spa treatments too relaxing to pass up. With new cruise ships setting sail at a regular clip these days, many cruise lines are dedicating resources to upgrading their existing fleets— Celebrity Cruises included. The first in a $250 million revitalization project of the cruise line’s five Solstice Series ships, Celebrity Solstice set sail for her inaugural season in Alaska earlier this month with my dad and I onboard. As soon as we embarked the ship in Vancouver, I knew I recognized her—my entire family sailed Solstice three years ago for an Alaskan celebration of my dad’s 80 th birthday. It was fun to happen upon some favorite spaces from that cruise, like the Sky Observation Lounge, Solarium, and Martini Bar, while discovering new spots like The Parlor with its sports bar vibe and games (Ski-Ball, anyone?), and the cozy Boulevard Lounge.…