Found this right here regarding the titanium.
In the US, 70% of all titanium is produced in the form of the exceptionally strong and tough 6Al-4V alloy (Titanium + 6% Aluminum + 4% Vanadium). It attains a strength of roughly 160,000 psi, making it about three times stronger than pure Titanium. Titanium's density is a little over half the density of steels (4.4 vs 8 g/cc) so a steel would need to have a strength of 290,000 psi to match the strength-to-weight ratio of Titanium. Only a handful of the most exotic steels can meet this standard and then, only after rigorous, technically demanding physical processing and heat treatments. The flip side of this is that the steels can be worked in a much lower strength condition while 6/4 Titanium is always quite strong and hard to form. As a result 6/4 Ti parts are always expensive. For instance you can get the slightly lower strength alloy 3Al-2V in 9mm tubing with a .6mm wall thickness for about $10/foot. Double that for 6/4 Ti even though 3/2 Ti is still about 130,000 to 140,000 psi strong.
Titanium's strength plus its corrosion resistance and weldability place it squarely into its own class. Titanium is resistant to corrosion by seawater, hot acid, body fluids, and a wide variety of industrial chemicals. It's often used in demanding applications from hip implants to entire submarines to the plumbing in caustic chemical manufacturing plants. Corrosion probably played THE justifying role in its selection for the above mentioned museum. Being a seaport, Bilboa has a far more corrosive environment than mere stainless steel can cope with. Pure titanium is a shoo-in compared to a nickel superalloy that could also handle the climate.