GIS Analyst here - to be perfectly honest, most GIS jobs these days are "something else" + GIS. So, an employer might advertise a position for a geophysicist and also want GIS experience. In fact, that's how I got into GIS in the first place (I was an environmental scientist (ecologist/biological technician) who started using GIS (ages ago) and it eventually transitioned into full-time GIS). That's not to say that there aren't pure GIS jobs - I work full time GIS and mainly do spatial analysis (which is varied and interesting) - but pure GIS jobs are often are very boring rote work (think working for the planning department at a city, for example). GIS programs want you to believe there are tons of high-paying jobs out there, but I would say that's largely not true, except for entry level jobs (that are not that high paying).
I personally would find an area you might really enjoy and add GIS on top of it. Employers really like that added value (because they don't really want to hire us dedicated GIS analysts anymore because we cost more). In addition, GIS certificates aren't that valuable (IMO) because you can get them with no real-world experience. We have hired people who supposedly had experience (from going through a certificate program) and they had to have a LOT of hand-holding. Just my opinion though. If you could get one cheaply, it might be worth doing just to get the software experience. A GISP is more valuable, but if you have no experience, you'd have to work up to that (it takes a lot of "experience" points).
If you think you would enjoy GIS you could get the personal edition of esri's ArcGIS Desktop - I think it is $100. (There are other software vendors, but esri is the biggest, and it is the one I am most familiar with. There are open source packages as well, though they have a steeper learning curve for a beginner.) Then do the free tutorials esri offers as well as any other tutorial you can find online. Use esri's forums (less helpful) or gisstackexchange (super helpful) for answering questions and figuring things out. Then just start using it in conjunction with whatever you are doing for your day job (or even just for fun!). It may not seem like there are many opportunities to use GIS in a non-GIS environment, but I think you'd be surprised. Almost everything has a geographic component, either inherently (ie environmental geography), or when viewed through, say, a sociatal or cultural geography lens. You could even make up data just to get used to working with the software. There's also a lot of free data out there that you could use. You won't be able to use it for your current job (probably), but it's the *doing* that's most important. Most GIS softwares are very complex and it takes a while to find your way around easily.
Other related industries you might explore: photogrammetric mapping (although this is dying out somewhat), image analysis (satellite, aerial, hyperspectral), LiDAR collection/processing/analysis (LiDAR has been and is still becoming more popular), drone (piloting, imagery/LiDAR/thermal/other data collection), mobile mapping (those big units you see on trucks that collect 3D data). Even getting a little experience in some of these gives you an advantage if you want to apply to a job that is "something else" + GIS.
Also, it is becoming increasingly important to have programming/scripting skills (Python in the case of esri) so that's worth investigating if you like coding. Web development is also becoming increasingly popular (web map and app development, for example). Server administration experience can be valuable. So can enterprise database (eg. Oracle and SQL Server) experience.
Once you get some experience you could volunteer through GIS Corps:
https://www.giscorps.org/A final word to the wise though - environmental engineering (what I do) with a big consulting firm can be... challenging. I have been in the industry for over 15 years, the last 10 with the same company, and though I make pretty good money, I've been doing it for a long time (or so it seems), and a lot of people don't make nearly as much. It can also be really stressful being in a seller-doer model environment, and the longer you are in the industry the more they want you to move into project management (something I am 100% not interested in). (I'm currently looking for an exit strategy.) This is not to discourage you from exploring these options, just a little heads-up. I'm sure there are people who are in the same position as I am that love it. YMMV!